tsukihi.me is one of the many independent Mastodon servers you can use to participate in the fediverse.
Tsukihime (月姫, tsu-kee hee-mei) translation means Moon Princess. This server is ran by a Type-Moon fanatic as a safe haven for trans people by trans people
Looks like the clothing and the art style are combining weirdly, this style of clothing has these pockets(? IDK what to call them) at the top of the arm and a tighter long sleeve below.