This article is about a/an ally in Kamen Rider Decade.

The elderly woman known only as Grandma (おばあちゃん Obaachan) is very tenacious and gives out advice to her granddaughter Mayu, despite her grandson having disappeared. Following monk-like philosophies of peace and spouting amazingly appropriate zen-like phrases, she runs the Tendouya (天堂屋 Tendōya, Heaven House) oden restaurant. It is later revealed that she is aware of her granddaughter being a Worm during her conversation with Tsukasa, and her grandson being Kabuto as she expresses her worries when ZECT finishes building the Clock Down system.

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