I don't know what the swimsuit is actually called. Personally, I call it "One String Swimsuit.

Link to いつも眠い's Pixiv:
https://www.pixiv.net/users/2757608

Edit 08/03/24 (mm/dd/yy):
+97 new images

Edit 09/01/24:
+63 new images

Edit 10/02/24:
+76 new images

One of my favorites, too!

Base +6, icontributenothing +19, thenewdrax +7, BlazinRoc +11