He is a ninja exorcist from the Kazamaki family and the grandfather of Matsuri Kazamaki.

Japan may be brimming with mysterious monsters called ayakashi, but they have a special exorcist ninja force to counter the threat! Young exorcist ninja Matsuri spends his days fighting ayakashi to protect his childhood friend Suzu. But when an ayakashi cat named Shirogane shows up, things get turned upside down! 
 
(Source: MANGA Plus)

Teenager Kazamaki Matsuri has long been part of an elite force of ninja exorcists, tasked with fighting malicious ayakashi spirits who threaten Japan–especially those after his childhood friend, the spirit medium Kanade Suzu. As he fiercely protects her, and his relationship with her blooms from friendship into something more, a powerful cat ayakashi vows to get between the lovebirds: by casting a forbidden spell that turns Matsuri into a woman! With no apparent way to undo the spell, Matsuri must continue battling ayakashi–and go back to school–in this new feminine body until he can find a way to turn back.
 
(Source: Seven Seas Entertainment)
 
Note: The series originally started serialization in Weekly Shounen Jump. It then moved to Shounen Jump+ starting April 25, 2022.

Seigen Kazamaki