Gen-An

Gen-An (Japanese: ゲンアン) is the elder of Izuna's ninja group. He think of Izuna as his granddaughter, a feeling she reciprocates and actually shows genuine affection for him even. He in turn takes care of Izuna. Despite being elderly, he remains in excellent shape. He's still walking on two legs and such, even capable of running around quickly.

Background
"He used to be the leader of our ninja village, but now he's just a vagabond. We call him "Grandboss." He treats me like I was his real granddaughter... Stay healthy Grandboss"

- Izuna (Izuna 1 Manual)

Apparently he disturbed some "sacred grounds" upsetting Takushiki, which is why he is inflicted with multiple curses.

Trivia
Gen-An is the boss of the Singularity Dungeon in Izuna 1.

External Sources
Character voice actor info. Izuna 1 official website (Japanese).