Yayoi Schwael began her career as the chief pilot of the white Core Robot Hartzenen in the Earth Defense Force until a combat-induced neural feedback injury permanently severed her synchronization ability. Kazuki Yotsuga’s intervention to commandeer Hartzenen and save her life ignited her unwavering romantic devotion, leading her to affectionately dub him her “prince.” Post-injury, she adopted a short hairstyle and pivoted to roles as a combat instructor, homeroom teacher, and tactical commander, strategically relocating her residence adjacent to Kazuki’s home. She engineered a covert passage into his bedroom, though Mitsuki Sanada repeatedly thwarted her advances.

Her grandmother, Mrs. Nanjoin, orchestrated marriage proposals to alternative suitors—a scheme amplified by Mitsuki’s meddling—but Yayoi’s loyalty to Kazuki remained unshaken. Even after reality merged post-Zinv’s destruction, she persisted as his homeroom teacher, habitually infiltrating the Sanada household through unorthodox entry points.

Expanded lore reveals her astral pattern’s recurrence across incarnations, linking her to figures like Amane Kaunaq, Gyokuren, and Mikami Kuramitsu. The Tenchi Muyo! GXP novels disclose her soul essence within the AI Fuku, devoid of memories, and a prior existence as Widow—a serial killer whose actions triggered mass casualties and psychosis. This lineage positioned her as an inadvertent catalyst for human cultural expansion via the galaxy-spanning Great Prehistoric Civilization, founded by Kazuki and allies.

Her character arc orbits relentless pursuit of Kazuki’s affection, leveraging professional authority, residential proximity, and clandestine tactics to embed herself into his life, undeterred by rivals or external schemes.