Mitsue Arihoshi, affectionately called "Obaba" (Grandma), is the elderly grandmother of Keisuke Arihoshi. She possesses extensive knowledge and experience of yo-kai and the supernatural. In her youth, Mitsue actively investigated yo-kai phenomena and battled malevolent spirits, gaining deep understanding of their nature and dangers.

She previously owned an older Yo-kai Watch and partnered closely with the yo-kai Whisper, relying on his research abilities. During this time, she confronted significant supernatural threats, becoming a formidable yo-kai investigator.

Decades later, as an elderly woman, Mitsue remains a crucial mentor. She recognizes the resurgence of dangerous Shadowside yo-kai and guides her grandson Keisuke after he obtains the new Yo-kai Watch. She provides essential historical context, explains Shadowside transformations, and offers strategic advice drawn from her past.

Her wisdom encompasses yo-kai lore, Yo-kai Watch functions, and tactics against hostile spirits. Mitsue maintains her connection with Whisper, who continues to assist her and later Keisuke, bridging past and present generations of investigators. She actively supports Keisuke's efforts, often deciphering cryptic yo-kai information or offering guidance during critical battles against powerful Shadowside adversaries.

Mitsue demonstrates resilience and continued dedication to protecting others from supernatural harm, leveraging her lifetime of accumulated knowledge to aid the new generation.