Tajimamori served as the former guardian of Yggdrasil, the tree of life. A millennium ago, he discovered Rin slain by bandits; a Time Fruit entered her body, granting her immortality, reviving her, and sparking her love for him.

Despite their deep connection, Tajimamori maintained only distant telephone contact with Rin for centuries. This separation persisted until the climax at Apos' castle, where he reappeared to aid Mimi and Mishio Maeno in locating the captured Rin. He revealed Apos' plan to sacrifice Rin to Yggdrasil to become its eternal guardian and opened a portal to the castle.

Reuniting with Rin at Yggdrasil, Tajimamori shared intimacy with her. Apos interrupted, killing Tajimamori and pushing Rin into the tree. It would later be revealed that Apos was Tajimamori's son, and that the Maeno family members—Kouki, Teruki, and Mishio—were Tajimamori's descendants through separate bloodlines.

Following Tajimamori's death, Rin gave birth to their son, a normal human boy possessing a natural link to Yggdrasil. This trait would pass through his descendants, paving the way for a future where humans understood and coexisted harmoniously with Yggdrasil.