The story centers around the lives of Kohaku, an angel, and Shuichiro Kudo, a mortal doctor. While walking home from work one day, Shuichiro notices Kohaku stuck on a tree and being attacked by a crow (who was actually sent by Koryuu the demon to attack her). He rescues Kohaku and in return, she offers to grant him a wish. However, Shuichiro is satisfied with his life - he has a decent home, money, good looks and job - so he does not want anything. However, Kohaku is honour-bound to grant the wish, so she stays with him.
The story charts how Shuichiro and Kohaku's relationship develops with the help or hindrance of other angelic, demonic, and mortal characters that they subsequently meet.
Although most resemble stereotypical bishōnen, the angels in Wish are genderless. However, in the English translation, they are assigned male or female genders, to avoid calling them "it". In the original Japanese, the demons refer to themselves using gender-specific personal pronouns and physically resemble one sex or the other. In the English version, they are given the gender most suitable for their personality.
Kohaku is a rather accident-prone angel who has come to Earth in search of her mentor, Hisui. When she gets trapped in a tree and attacked by a crow, she is rescued by Shuichirou, a young doctor. As a result, she feels indebted to grant him one wish but finds the kind doctor is satisfied with all aspects of his life. Thus, she remains with Shuichirou in hopes of repaying him somehow (subsequently getting in other sticky situations as a result).
Because she is only a trainee angel, Kohaku can only maintain a full-size form during the day - at night she shrinks and is only about a foot tall, looking rather like a chibi character. As an angel, she cannot consume anything that came directly from a living organism (ie meat, vegetables, bread) with the sole exception being milk and occasionally honey.
Eventually, God forces Kohaku to return to Heaven, despite her debt to Shuichiro, because she is the only angel capable of singing to the Tree of Life, from which new angels will hatch from. However, her affection for Shuichiro has grown so strong that she returns to Earth without God's permission. As a result, God strips away her powers for 100 years. This is not a punishment; Shuichiro dies shortly afterwards and the loss of Kohaku's powers means she can sleep for the 100 years it will take for Shuichiro to be reborn. At the end of these 100 years she reawakens and lives happily ever after with the new Shuichiro.
Kohaku is rumored to be modeled after Noriaki Kakyoin from JoJo's Bizarre Adventure.[original research?]
Shuichiro Kudo I
The first Shuichiro Kudo is a young doctor who rescues Kohaku from the tree where she is trapped. For this he is granted a wish, but isn't interested as he has everything he wants.
Shuichiro is generally kind and trusting, but isn't one to seek other people's company - something that is remedied throughout the course of the story by the two angels, two demons and two servant demons who all move into his house.
However, when Kohaku is called back to Heaven she realizes how much she is in love with him, and when he comes back he makes his wish - for Kohaku to stay with him. Shortly afterward, he dies unexpectedly (cause unknown).
He is rumored to be modeled after Jotaro Kujo from JoJo's Bizarre Adventure.[original research?]
Shuichiro Kudo II
The other Shuichiro Kudo is born 100 years after the last one was, and has the same soul as the previous one (reincarnation).
This Shuichiro is a student at the time he appears in the story, and comes across the house where he lived in his previous life. Kohaku then appears, offers to grant him a wish in place of the one he couldn't fulfill for his past self, and asks to be with him. Despite having no memory of his old self and hence no memory of Kohaku, he quickly gets back into the swing of things and asks to be with Kohaku. And so they live happily ever after.
Hisui is one of four Angel Masters of the four natural elements (fire, water, earth, and wind), her element being wind.
Hisui is the original reason Kohaku comes to Earth the first time, as the Angel Master disappeared during a meeting at the bridge between Heaven and Hell. She eventually reveals herself to Kohaku, and also reveals that she has made love with Kokuyo (Prince of Hell) and states that she and Kokuyo cannot return to Heaven or Hell because of it.
Shuichiro offers to let Hisui and Kokuyo stay in his house, and this is where they stay for the next 100 years after pledging to look after the sleeping Kohaku.
Koryuu is the demon equivalent of Kohaku - he can only maintain a full-size form at night, and at daytime is only about a foot tall. Koryuu's attitude toward Kohaku is a bit of a mystery, as he in turns helps and hinders Kohaku (friendly rivalry). One of Kouryuu's favorite pastimes is making Kohaku's day utterly miserable, and he derives great pleasure from seeing Kohaku sad. However, his attitude is later revealed to be a crush and he picks on Kohaku needlessly because of it (much like how adolescent boys do with crushes). This is made more apparent when Kohaku is stripped of all powers as he is furious over Kohaku's fate (especially after Shuichiro dies).
Koukyou is one of the sons of Satan, and falls in love with Hisui. As stated in Hisui's entry, he and Hisui start living at Shuichiro's house, and watch over Kohaku when she sleeps. Kokuyo is also aware of the first Shuichiro's impending death, but God stops him from telling anyone else so as to make sure things go as they should.
Ruri and Hari
Ruri and Hari are identical twin cat-demon underlings of Koryuu. They can transform into ordinary house-cats to hide from the world (during the day they must stay in their cat form, similar to the way Kohaku and Koryuu turn small), and will do anything he asks of them to get gifts (often sex) and/or souls. They deeply enjoy kisses from their master. You can tell them apart only by their jewelry - Ruri wears circles on her earring and necklace (earring and tail when in cat form), and Hari wears bars on hers.
The Master Angel of Water in Heaven. Touki has a reputation for being cold-hearted, mostly because of the hardened look that's always on her face. She first appears to see why Usyagi hasn't returned to Heaven and ends up bringing Kohaku back with her. She is very fond of Kohaku and protective of her in her own silent way. She has a very discreet relationship with Ransho and though she is very shy with her feelings for him and does genuinely care about him.
The Master Angel of Earth in Heaven. He comes off as one of the most easy-going Angels in all of Heaven despite his status. He loves to tease Kohaku and he's open with his affection for Touki. Like Touki, he's very discreet about their relationship but he can admit he loves her. But his loyalty to God is unwavering and he's not hesitant in delivering punishments handed out (as with the cases of Hisui and Kohaku).
The Master Angel of Fire in Heaven. He's got a very hotheaded personality and is quick to act before thinking. He's madly in love with Hisui and is convinced she was kidnapped out of Heaven. He often goes on rants about Hisui in the presence of the other Angel Masters, and Ransho often leaves Touki to deal with it. When he finds out Hisui left of her own volition and is deeply in love with Kokuyo he's very hurt by it, but he wants Hisui to be happy and lets her go, though he vows to hate Kokuyo forever.
Usyagi, though it says nothing within the four-volume manga, plays a very important role. Usyagi is a small white rabbit with wings. It relays messages from God - if it visits you, you are getting a message from God himself. The messages it delivers look like flowers, that dissolve and automatically implant themselves in the receiver's mind. Usyagi relays messages from Kohaku to God and back throughout the series.