Yoriko Yasaka is Mahiro Yasaka's mother. Her strikingly youthful look frequently causes others to doubt she could have a high school-aged son. Professionally, she works as a monster hunter, a career launched during her college years. She initially hid this occupation from Mahiro, revealing the truth only upon her return home during the series' events. Her primary weapons are throwing forks, which she wields with significantly greater skill and carries in larger quantities than her son, deploying them effectively against hostile entities when needed.

She maintains a welcoming and accepting stance towards non-hostile aliens, allowing Nyaruko, Kūko, and Hasuta to live in the family home despite their extraterrestrial origins. She supports their romantic pursuits involving Mahiro, though she first advised Nyaruko to temper her aggressive advances. Her position evolved to explicit approval of Nyaruko and Mahiro's relationship following a rescue operation where they played key roles.

Beyond monster hunting, she harbors a deep enthusiasm for video games, frequently purchasing new gaming consoles when returning home from missions. A recurring behavior involves hugging Mahiro, an action she describes as replenishing her "son-onium" levels, a habit persisting throughout her appearances.