>>536629953
He has problems.
Anyway, you can find most of his MegaTen art on his pixiv, including some for the guidebooks and TTRPGs.
https://www.pixiv.net/en/users/2042453
By the way, his nickname is かっちん (Kacchin) which is a cutesy way to call him but he explicitly chose ちん (chin) over something like ちゃん (chan) probably due to it sounding like ちんぽ (chinpo, penis).