Haruki Shiga (しがはるき, Shiga Haruki) is the main protagonist of the I Want to Eat Your Pancreas series and the first person to discover Sakura Yamauchi‘s secret. He is Fuyu's father in a sequel novel of the story.
Haruki is a plain-looking high school student that often wears a listless expression (at least according to his fellow classmates). His hair is jet-black and styled in a way that often occurs when males let their hair naturally grow and not style it, adding to his overall common and simple appearance.
He is often seen wearing his school uniform consisting of a pale beige blazer with brown details, a white shirt, a blue necktie with black dress pants and dark brown loafers. Otherwise, he seems to be wearing plain colored t-shirts and plain outfits that don't really make him stand out.
At the start of the story, he is anti-social and listless. He hardly portrayed any emotions in the story. As the story continues, it is shown that he is a coward and is afraid to have any relationships as he doesn't want him, and others to get hurt by his actions. But at the end of the story, he learns how to be more honest with his feelings. He seems kind, grateful to others. Throughout the story with the help of Sakura, he learns how to express himself and interact more with people. He learns how to care for people, love and be loved by people. It is during this change where he somehow starts revealing his true feelings towards Sakura.
Haruki is first seen putting books back with Sakura, who tells him about a superstition she believes in. She tells him about a superstition where if you ate someone’s organ, it would rid them of that organ’s disease. Haruki suggests that she follows the library rules as she was being incredibly loud.
After this, we are brought into a flashback where Haruki finds a strange book sitting on a chair in the hospital. The words on the cover read, Living With Dying. He opens the book to read it, and learns that the owner has a terminal illness and will die soon. He is then greeted by Sakura, who tells him that she owns the book. She is thankful that Haruki has found it, and told Haruki that she was scared she lost it. Sakura then tells him about her pancreatic disease and asks him if he’s surprised, to which Haruki replies by giving her a blunt answer and leaving.
The next day, Sakura invites Haruki to eat Yakiniku and Offal with him. While there, Sakura talks about the superstitious religious act of eating someone else’s organ, as well as what her favourite foods are. As they’re leaving, they pass through a market, where they see a man acting very rudely towards an elderly woman. Sakura then runs towards the man, calling his attention, then lands a swing kick on his crotch. While the crowd chuckles, Sakura grabs the hand of Haruki (who is surprised by her actions) and drags him away as they escape from the authorities.
The next day, Sakura invites Haruki out to eat Yakiniku and Offal again. While they’re there, they are seen by Sakura’s best friend, Kyouko Takimoto, who assumes that it is a date. She warns Sakura and tells her that there are better guys in her league, but Sakura turns her down and says they aren’t dating. During their break time in school, Haruki watches Takahiro approach Sakura to give her a ‘super rare CD.’ He overhears a group of girls saying that Takahiro is the class rep and that he’s very popular among girls, having girls fawn all over him all the time. Sakura and Haruki then visit a cafe after school where she tells him that she had recently broken up with a classmate.
The next day, Issei Miyata eventually approaches Haruki, asking him if he’s dating Sakura. Haruki turns him down like he did to the others. Eventually, Kyouko arrives and beats him for slacking off instead of cleaning. When Miyata leaves, Kyouko shoots an aggressive glance at Haruki.
With the school break nearing, Haruki joins Sakura on a trip. Haruki tells Sakura that he didn’t bring any extra clothes, and Sakura tells him that he can buy some when they arrive. While on the train, Haruki asks Sakura how she got her parents to agree with her going on a trip, and Sakura says that she tricked them about having a sleepover at Kyouko’s and that she would cover for her. Upon figuring out that Haruki committed the same act, she tells him how sad it is not having any real friends. Sakura then opens her diary and asks Haruki for his name. Haruki tells Sakura his full name, though it is silenced to the audience. Upon arriving at the hotel, Sakura is shocked to discover that she and Haruki were booked into the same room, but a higher one instead. Upon arriving in the hotel room, Sakura immediately goes to the bathroom to take a shower. However, she forgets her facial lotion and calls Haruki to get it for her. Upon opening her bag, however, he is astonished to see several packs of pills and syringes. Despite this, he retrieves her lotion and places it on the bathroom floor. After Haruki has his bath, he comes out to Sakura saying she brought drinks. Upon taking a sip, he realizes that it’s alcohol. Sakura then proposes that they play Truth or Dare, except by using cards with a similar nature as the game. Sakura first asks Haruki which girl he finds the most attractive in their class, to which Haruki replies that he likes the girl who’s good at Math. She then asks Haruki where he would rank her based on attractiveness in their class, and Haruki says he would rank her around third based on everyone he could remember. Haruki then asks what Sakura was like as a kid, where Sakura tells him that she was more of a problem child. The game goes on with the two learning more about each other, where Sakura eventually revolts by asking if it was an interview. Sakura’s next turn presents Haruki with two pre-determined choices; either state three things that he found cute about her or carry her to bed. Haruki quickly offers her his hands instead, but Sakura turns him down. He then proceeds to carry her to bed, with Sakura blushing as he sets her down. With Sakura’s turn being the next one, she asks Haruki what he would do if she admitted to being scared of dying, to which Haruki flashes back to the enormous hound of medication he saw in Sakura’s bag. He then decides to dodge the question by picking Dare instead, where Sakura tells him to accept the dare with no objections. She then tells him to climb into bed with her, which Haruki does without complaining.
While on the train home the next day, Sakura asks Haruki if he enjoyed the trip, and is surprised when he says yes. Some time after that, Haruki is approached by Kyouko while on the balcony while reading, and she asks him why he had gone to the trip with her. When Haruki doesn’t answer, she hits his book away from his hand, causing it to fall down onto the floor and get soaked with rain. She aggressively warns him about Sakura being fragile and prone to crying. She explains to him that Sakura cried for days after a breakup she had in Junior High. She then ends the conversation by threatening to actually kill him if he did something to Sakura.
While working in the library, Haruki discovers that Sakura’s favourite book is The Little Prince. After finishing work in the library, Sakura invites Haruki over to her house so she can lend him her copy of The Little Prince, where they spend hours chatting and playing video games. When Sakura asks Haruki if he has a crush on her, Haruki uncomfortably denies it and stands up to search for her book on the bookshelf, but is then hugged by Sakura who tells him that she’s always wanted to do something naughty to someone. As she leans closer to kiss him, she then stops and backs away, laughing and giggling and telling him she was only joking. Haruki then angrily pushes Sakura down on the bed while gripping her wrists very tightly. Sakura then becomes terrified and tells him to let go of her while crying. Realising his mistake, Haruki stood up, grabbed the book from her shelf and disappeared out the door, leaving Sakura alone. When Haruki exited the gates of Sakura’s house, he opens his umbrella to avoid from getting soaked in the rain. He notices Takahiro walking nearby, who asks him why Sakura fell for him, to which Haruki replies that their relationship wasn’t what he thought it was. Thinking it would help Sakura, Takahiro punched Haruki in the face, causing him to fall onto the ground. Sakura then suddenly bursts from inside and gets down to help Haruki. When she asks who had hurt him, Takahiro pridefully admits to punching him. Sakura then gets furious and tells Takahiro that she hates him, shocking him. He angrily turns around to leave. Haruki then tells Sakura that she should be with someone who truly cares about her as their meeting was purely a coincidence, and Sakura denies this and tells him that all their actions were made purely so that they would meet each other, and backs this up with an apology.
Several days pass until Haruki meets Sakura in the hospital. She sees her dancing in her room, and when she turns around to see him, is embarrassed that he had seen her. She retreats to her bed and tells Haruki that she was only in the hospital because some of her numbers were off, and they start playing with a set of cards while they discuss why the class thinks that Haruki is stalking Sakura. Sakura then stands up to look out the window, with Haruki thanking her for teaching him so many things. Sakura accepts this by giving him a warm hug. Kyouko then suddenly enters the room, and is angry when she sees them hugging. Sakura then distracts Kyouko, buying Haruki time to escape. During the night, Haruki and Sakura watch the fireworks festival together from the rooftop of the hospital. Haruki confesses to Sakura that he is worried about her and wants her to live. The fireworks then begin with Sakura enjoying them as they give each other a warm hug. Sakura then promises to go to the beach with him once she is discharged. They plan to meet at the cafe they had went to previously on the day she discharges.
On the day, Sakura discharges, Haruki makes his way to the cafe where he is supposed to meet Sakura. On his way there, he passes by Miyata who chats with him and offers him some gum. Haruki watches as Miyata is surprised by his younger siblings, and walks on ahead. When he arrives at the cafe, he and Sakura text using their phones where she asks him for a compliment, Haruki having made a ‘mean joke’ to her. Haruki then waits for a long while, but Sakura doesn’t arrive. She then texts him and apologizes for being late, having just left the house. Haruki considers what to type for a while and thinks about how much he had changed because of her. He typed out "I wish I can brew a potion from the dirt under your nails,” then immediately deleted it, to replace it with the words, “I want to eat your pancreas.” He then sends her the text message. Sakura did not respond and also didn’t meet with Haruki that day. Worried, he returns home.
While having dinner that night, Haruki sees Sakura on the news, her being a victim of a homicide, having been stabbed in the chest and lying unconscious on the ground. A rescue attempt by an ambulance had failed and she inevitably died.
Haruki is next seen at home, being too devastated to go to her funeral. Haruki then visits Sakura’s mother, asking if he could borrow her cellphone. Sakura’s mother recognizes him as Sakura’s ‘special friend,’ saying that she told him that someone would come to get her Living With Dying. She gives Haruki her cellphone and journal, and Haruki discovers that Sakura had received his message. He then reads her journal, which results in him crying upon reading the last entry. He thanks her mother, who says he can take her journal home. Afterwards, he invites Kyouko over to the café where he was supposed to meet with Sakura several days earlier, and talks to her about Sakura and her disease. Kyouko gets angry at him for not telling her, to which Haruki hands her Sakura’s Living With Dying, causing Kyouko to cry after reading it. Afterwards, he asks Kyouko to be his friend.
The story ends with Haruki and Kyouko visiting Sakura’s grave together, hinting that the two finally became friends. They leave Sakura some flowers and Kyouko offers Haruki some gum as they leave to visit Sakura's home to see Sakura's family. While they’re leaving, Haruki smiles, and a leaf of a Sakura tree slowly falls down and lands on top of Sakura’s tombstone. (That sakura leaf represents Sakura watching over him).
After story 
After a considerable number of years has passed. He has a wife and a daughter named Fuyu. As usual, he always go visit Sakura's grave regularly. After overhearing his phone call, his daughter got suspicious of him and thought he having an affair. Fuyu decides to follows her father to with her friend, Anzu to figure out what he is up to. After a few misunderstandings, he explained his relationship with Sakura to Fuyu. The story between them has changed his daughter's perspective in life as she always claim that life is boring and hers is very average and nothing special.
Although Haruki initially disliked her at first, the two appeared to have an awkward relationship at the start of the series. However, Haruki starts to get used to Sakura’s rambunctious nature and appears to start to develop feelings for her. Mere moments before Sakura’s death, he sends her a text message saying "I want to eat your pancreas", proving his feelings for her (due to a superstition/religion, it is believed that eating a part of someone's body will allow their soul to live on inside yours). Sakura knew the reason why he wouldn't call her by her name as by doing so it would advanced their relationship which would cause him to get hurt even more after her time as come. He eventually came to realize he did love Sakura and that he had always been harboring his romantic feelings for her.
After a number of years, Fuyu asked Haruki whether he liked her. He states, “We weren’t friends, neither family nor lovers. She said we got along, but I think even that’s a bit off.” Fuyu didn't understand what he meant. Haruki explained that no one really understood his and Sakura's unique relationship. That their relationship was beyond being just mere friends or lovers, that they were more like soul mates.
Kyouko immensely disliked Haruki at first, though the two eventually come to terms with each other after Sakura’s death and become friends. They visit Sakura's grave together and afterward visit Sakura's family.
Miyata can be seen casually chatting and having friendly conversations with Haruki while offering gum and seems be interested in his (Haruki’s) and Sakura’s love life.
Takahiro is jealous of Haruki’s and Sakura’s relationship which results in him physically attacking Haruki.
Their relationship is like a how a typical father act towards their daughter, but their relationship strained a bit after she suspects him on having an affair and the argument they had over the value of life. After her father shared Sakura's story and through their meaningful conversation, both became closer than before.
- The live-action movie actually portrays Haruki's life 12 years after Sakura's death. While the manga and the anime only time skip 1 year after.
- The knowledge of Sakura's death in the live-action and the anime/manga are at different places. One is outside a shopping mall while the other is at his own house.
- He got inspired to become a teacher after Sakura encourages him to be one.