Suikakasen 1
In the Year 794, when youkai existed alongside humans, leader of the oni bandits Suika Ibuki is squaring up against her friend and fellow oni Yuugi Hoshiguma for a sparring match. Kasen Ibaraki, a child oni, gets annoyed at this and yells at the two to not fight. Suika and Yuugi cheekily explain that they're not going to fight, but rather play an intense game of rock-paper-scissors, which Kasen happily accepts. The two begin to "play" their game, which ends up destroying most of the area they're in, much to Kasen's delight. After the fight, Suika declares that they now do a drinking match.The scene flashbacks to a then-human Kasen, with noticeably scaly-like skin and fangs, sitting alone by herself near a tree. Douji Ibuki, a large oni, approaches Kasen and mocks her ghastly appearance and for seemingly having been abandoned by her parents. Kasen, in response, throws a mud ball at Douji and tells the oni that she's waiting for her mother, who promised to return for her. Douji simply smirks before fading away, telling the child that she'll die and that her mother will never return. As time passes, Douji watches as Kasen continues making mud balls while getting weaker from starvation. After some time, Douji approaches the dying child and asks why she continues making mud balls when she cannot eat them. Kasen explains that she makes them because her mother would pretend to eat them and say they were delicious. Finding this ridiculous, Douji reveals herself to be Suika and eats one of the mud balls, predictably finding it disgusting. Despite this, she takes pity on Kasen as she realizes how much her mother must have loved her. Suika drops the Hyakuyakumasu, an oni treasure, in front of Kasen and explains that drinking from it can heal the body at the expense of turning into an oni. She offers the child a choice; either die as a human without seeing her mother, or turn into a youkai and continue waiting for her. Kasen readily accepts the Hyakuyakumasu and drinks from it, gradually turning her into an oni. In the present, Suika tells Kasen that a lifetime of joy awaits her as part of the oni bandits.note
Several information is given about Suika and her posse: she was revered as a mountain goddess and she and her bandits would go around causing mischief and kidnapping people. Eventually, the humans fought back by weakening the oni bandits with poisoned sake and attacking them with legendary swords. As a result, most of the oni were wiped out, Kasen's right arm was severed, and Suika's gang ultimately fell in power.
Suikakasen 2
Following the attack on the oni bandits by the humans, Suika is seen crying and drowning her sorrows about her defeat while a nearby Yuuga tells her to calm down. Suika blubbers about how Kasen left to retrieve her arm and become a full oni again, yelling for her to come back soon. Kasen, who had broken off her oni horns and covered them in an attempt to appear human, stands near an invisible barrier that separates her from the human city. She attempts to pass it only for it to severely damage her functioning arm. Healing herself with her Hyakuyakumasu, she laments how being cut by that legendary sword has prevented her right arm from growing back.Kasen notices a young woman nearby recite a poem, and touched by it, answers back with a poem from herself. The poet compliments Kasen's poem before pointing out that she's not a human. Instead, the poet assumes that Kasen is a hermit, which she quickly denies. Despite this, the poet is insistent that Kasen is a hermit and gets excited. Kasen attempts to fly away with an eagle, but the poet latches onto her and prevents her from escaping. The poet introduces herself as Yoshika Miyako and begs Kasen to teach her how to become an immortal hermit. Kasen, who's been bound to a tree, makes it very clear that not only is she not a hermit, but she has no interest in helping Yoshika with her outrageous plea. As Yoshika unties Kasen, a thought comes to the former oni; she can use Yoshika to find a way into the city and retrieve her arm. Kasen goes back on her word and agrees to help Yoshika become a hermit, much to the latter's delight. Yoshika eagerly buys several books on how to become a hermit, and Kasen uses a spell to give herself a bandaged prosthetic arm. As Yoshika's training starts, Kasen at first is only interested in figuring out how to cross the invisible barrier. However, as time goes on, she begins to form a friendship with Yoshika. One night, while sitting alone, Kasen wonders to herself why she's becoming close with a human when Yuuga appears. Yuuga explains that she, Suika, and the rest of the surviving oni are heading to a deserted mountain, and asks Kasen if she's coming with them. Kasen declines, explaining that she wants to find her arm and become a full oni again before rejoining the others. Understanding this, Yuuga wishes her luck on her journey.
Flying to a mountainside with Yoshika, the poet rests her head on Kasen's lap as she admires the view. Having already found a way past the barrier, Kasen decides to kill Yoshika so as to not become any closer to her. Right as she prepares to kill Yoshika, she's stopped when the poet begins to cry as she talks about how grateful she is to meet someone like Kasen. Yoshika confesses that the reason she wants to become an immortal hermit is because she's terrified at the thought of dying young. Hearing this, Kasen apologizes and confesses to Yoshika that she was just using her as a way to get through the barrier, and reveals herself as a former oni who now doesn't know what she actually is. In response to this, Yoshika simply stuffs a peach into Kasen's mouth and suggests that if she doesn't know who she is, she should become a hermit like her so that they can remain friends. Kasen cries happily at Yoshika's kindness and promises to become a hermit like her. After some time, Kasen was able to cross the barrier, but could never find her arm. Having lost contact with Yoshika, Kasen still kept onto her promise of becoming a hermit, hoping to one day reunite with her friend.
Suikakasen 3
Yoshika is seen meditating as she trains to become a hermit, having a flashback of when she witnessed a deceased person as a child and seeing the lady with her, presumably her mother, crying. As she meditates, Seiga Kaku, a Taoist hermit and Yoshika's current master, appears behind her and playfully covers her eyes. Seiga invites Yoshika to dinner, and the two reminiscent about their meeting, which was humorously similar to how Yoshika met Kasen, and Yoshika remarks how incredible it is that Seiga is an acquaintance of the Great Hermit. At the dinner table, Yoshika marvels over the diverse array of dishes as Seiga explains that this is a celebration before she introduces Yoshika to a reikon, or a spirit of noble status. As Yoshika uncovers her dish, she's shocked to find a severed human head on her plate. Yoshika questions Seiga about this when a second Seiga approaches from behind her. This Seiga points out how the severed head in front of her is no different from the meats on the table, as both were made from former living beings. Seiga remarks that humans, like many other living beings, must kill and eat other living beings to survive, though humans are especially cruel since they cut, cook, and prepare the corpses they eat. As such, hermits like themselves mustn't forget to appreciate their own lives. After a tense moment, Seiga cheerfully reveals that the entire thing was just a prank she pulled on Yoshika, and that the severed head and second her are simply puppets. Yoshika congratulates Seiga on her performance and the two begin to eat. As they eat, Seiga remarks how unfazed Yoshika was by all this, and wishes her luck on her meeting with the reikon.The next day, Yoshika meets with the reikon, though it's apparent their meeting did not go well. Seiga find Yoshika hiding inside a closet in tears, and laments how the reikon did not deem her suitable to be a hermit. When Yoshika says that she must become a hermit, Seiga grabs her hand to reveal blood on it. Seiga realizes that Yoshika is dying of a terminal illness and carries her over to a bed, sorrowing how her short lifespan has made it impossible for her to become a hermit. Yoshika disagrees, explaining that while at first she clung onto stories of becoming a hermit in her desire to not die, it was her meeting with Kasen that gave her to motivation to become one. Explaining her promise with Kasen to reunite once they became hermits, Yoshika pleads with Seiga to make her into a hermit. Seiga, touched by Yoshika's story, agrees to speak with the reikon once more. She offers Yoshika a medicine known as Tan'yaku, telling her that the drug will help turn her into a hermit. Yoshika thanks Seiga for the medicine and takes it, promising Kasen to meet with her again one day.
A flashback is shown of Seiga's previous life while living in China. Wanting to become a hermit, Seiga would study the scriptures of her father day and night. One day, while waking up, Seiga was shocked to find a random man sleeping beside her, who suddenly professes his love for her. That man, Kan Kaku, had fallen in love with Seiga at first sight and used a magic chisel to bore a hole in her wall to meet her. While Seiga is at first obviously not thrilled at this rather unorthodox confession of love, the two eventually married, and Seiga soon began to genuinely love Kan. However, years later, Seiga suddenly passed away, devastating Kan. While walking along a mountain path, Kan wandered into a cave and, much to his surprise, found his wife alive and well. In order to become a hermit, she had to fake her death and live with her father in the Hermit World. Kan rushed to embrace her, but Seiga quickly pushed him away, apparently having chosen being a hermit over her husband.
Back in the present, a now deceased Yoshika lays in bed with blood covering the bed sheets. Seiga appears to be mourning her death, only to reveal that she's actually crying from laughter. Seiga insults and cruelly mocks Yoshika for trying to be a hermit for someone else's sake. However, having taken a liking towards her, Seiga decides to keep her promise of giving life to Yoshika. Using Yoshika's blood as ink, Seiga draws an ofuda and attaches it onto Yoshika's face, transforming the dead poet into a jiangshi. 1,200 years later, Seiga takes Yoshika to the scene of a battlefield in the outside world. She comments how humans have now begun killing each other for reasons besides eating each other, and refers to them as pests infesting this world. She remarks how witnessing scenes like this as an immortal hermit would surely darken one's heart, and tells Yoshika not to have her heart tainted by this. Eventually, Seiga would meet with Kasen and, believing her to be another hermit, decide to work with her.
Suikakasen 4
Years have passed, and most youkai and non-humans from the outside world now live in an area known as Gensokyo. Kasen, now a resident of Gensokyo, walks to a gate which looks similar to the one where she met Yoshika and remarks how in the end, she was never able to find her arm nor reunite with her friend. Suddenly, Suika appears behind Kasen, much to the latter's annoyance. Suika reveals that she always knew about Kasen and Yoshika's friendship, and when Kasen mentions if she had any objections to it, Suika shouts angrily that she did. Now riled up, Suika throws a rock at Kasen and begins to fight her. As they fight, Suika comments that Yoshika is most likely dead after all these years, and tells Kasen to give up on finding her. Kasen denies this and makes it clear she intends to keep her promise, summoning various animals to keep Suika down. Suika, in turn, transforms into a giant and smashes Kasen into the ground. An injured Kasen lays immobile as her left arm is severed by a falling rock. Suika approaches Kasen and boasts about how Kasen stands no chance in defeating her, before healing her by having her drink from the Hyakuyakumasu. Now healed, Suika proceeds to beat Kasen up again, intending to beat her until she gives up on her promise with Yoshika.Kasen, however, begins asking Suika why she knew that the Hyakuyakumasu would transform one into an oni, and asks her when did she become an oni. This questions enrages Suika, who throws Kasen to the ground and confesses that, like Kasen, she was once an abandoned human child formerly known as Sute Douji, or Throwaway Kid. However, unlike Kasen, she's fully moved on from her past as a human. Suika conjures up a fireball and throws it at Kasen, only to miss. She tries again and misses once more, before asking why she sees two Kasens. Kasen reveals that she secretly swapped Suika's sake with the one that was used to poison her many years ago, rendering her incredibly drunk. However, Kasen admits she didn't account for Suika unintentionally making her drink the poisoned sake as well, causing her to be drunk as well. As the two drunken girls fight, Suika attempts to convince Kasen that she's only hurting herself by holding onto promises she knows will never be kept, and that she should just forget about Yoshika and go back to living a carefree life like they used to. Kasen proudly proclaims that Yoshika saved her by healing the wounds she had as a child, and for that, she will never abandon her friend. Suika, now even more enraged, goes all out against Kasen, and the two deliver a devastating punch towards each other. In the end, Suika is knocked several feet across the ground, and Kasen has passed out from overexertion. Suika admits that she's actually envious that Kasen is able to hold onto her promises for so long, when she herself had given up on hers.
Two days later, a now sober Kasen is walking through the woods, still affected by Suika's words that Yoshika is most likely dead. As she's walking, Kasen is shocked to see Yoshika standing in front of her, and quickly runs to embrace her. At first, Yoshika asks who Kasen is, and Kasen explains that Yoshika just reminded her of an old friend. Yoshika quickly remembers who Kasen is, and regains her humanity as the ofuda on her face falls. The two friends cry as they embrace each other after so long. The ofuda flies into Seiga's hand, and while saddened that Yoshika can no longer be with her, she allows her to spend her last moments with her friend. Suika comments how Seiga doesn't seem the type to care about other people, especially with what she did to Yoshika. A flashback reveals that when Seiga rejected Kan after he found her, he used his magic chisel to follow her into the Hermit Village. Eventually, Seiga came back to Kan, and the latter became a hermit so that the two could live happily together. Seiga cries as Yoshika's reunion with Kasen reminds her of her past love with Kan, and she, Suika, and Yuuga laugh it off as they watch their pupils reunite.
Kasen carries the weakened Yoshika to a flower field and lays her on the flowers, where she enjoys the feelings of the world after so long. Kasen asks her friend what she wants to do next, and Yoshika simply asks her to lay by her side. The two begin to sing with each another and reminisce their friendship before Yoshika finally passes away. Though saddened, Kasen embraces her friend and wishes her farewell. Kasen sets up a gravestone for Yoshika at the Sanzu River, with Suika even coming by to pay her respects. Years later, as Kasen is visiting the Sanzu River, she sees Yoshika, now a ghost, happily waving at her. Kasen smiles as she's finally able to be with her friend once more.
