Yaku Yakuzen

Yaku Yakuzen is a uniquely charming member of the Rentarou Family. In her youth, she served as a military medic, acquiring extensive knowledge and experience in medicine. Although she shares a highly similar, child-like appearance with her granddaughter Kusuri—complete with traditional kimono and wooden sandals—she possesses the wisdom and mind of an elderly woman. Because she ingested a highly potent prototype of the immortality drug, her child-like body cannot be reverted with neutralizing medicine. In daily life, Yaku exhibits a warm, grandmotherly presence, deeply caring for the other family members as if they were her own grandchildren. She is famously clueless about modern technology, often referring to smartphones as "planks," and harbors a slight fear of automobiles. When interacting with Rentarou, she balances her mature wisdom with a mischievous, teasing attitude, using her archaic speech pattern to bring playfulness to the group.