Per Wikipedia, Yami to Bōshi to Hon no Tabibito (ヤミと帽子と本の旅人?,
translated as Darkness, the Hat, and the Travelers of the Books), also known as
Yamibō/Yamibou for short, is a Japanese adult visual novel published in December 2002 by Root. A 13-episode
anime series produced Studio Deen aired between October and December 2003. Although the characters and their relationships remain
basically the same in the game and anime, the storyline is quite different.
This anime adaptation was recently added by Hoopla Digital as part of their television anime offerings under the shortened title
It involves a main heroine character, Hazuki Azuma (東 葉月 Azuma Hazuki) engaging in a search across various dimensions for her lost younger sister, a mute girl named Hatsumi Azuma (東 初美 Azuma Hatsumi?), who completely disappeared the night of her 16th birthday bathed in a mysterious green light!
The episodes are reminiscent of the old science fiction live action show Sliders. However, the younger sister’s own story is more like that of
Quantum Leap, for she is actually the biblical Eve, but assumes a new persona in each new “book world” she enters to engage with. The older sister is aided by Eve’s sister Lilith, who is, like Eve, depicted as a good witch wielding powerful magic. The main character’s younger sister was but one of these assorted personae of eternal Eve.
Lilith and her companion cockatiel, Ken (ケン), especially are the comic relief of the show. Hazuki eventually catches up with Eve, who is actually able to speak. Eve explains she cannot go back to being Hazuki's little sister but when Hazuki threatens suicide from having a broken heart, Eve reluctantly agrees to be reborn as Hazuki's daughter in the future. It's a strange relationship because Hazuki's feelings for Hatsumi are clearly overtly sexual and erotic and romantic. Lilith seems bisexual and flirts with Hazuki in a teasing manner but Hazuki rebuffs Lilith's advances and stays focused on her beloved Hatsumi. The various characters are redeemed by being granted a "do over" at very critical decision points in their lives. For her part, Hazuki uses her second chance to finally kiss her beloved Hatsumi, who reciprocates. Hatsumi still disappears the night of her 16th birthday, just as in the first time continuity, but Hazuki is at peace with this because at least she finally got to kiss her beloved and show the depth of her feelings for her....and she hazily remembers the promise Eve made to be reborn to Hazuki as her daughter in the future, which Hazuki accepts and looks forward to.
It's a very entertaining series but also quite strange. It is a sub-only show, no dub was ever produced, to my knowledge.