Since there's no other way that I know of to contact Pior (friend request was declined), I'm posting this here to hopefully bring this to their attention.

https://twitter.com/pafuhana1213/status/1384505100580786180

6 seconds into the video you see a cutscene with an npc with the helmet.

website: https://www.bocchi-neko.com/soldat

If Pior is already aware of this and/or they have given permission for use of the helmet in that game, then feel free to ignore this post.