I looked into the files and stuff and messed around with some textures using Special K.
This game is going to need an unpacker and some mesh edits to get the characters to be naked. Hilda specifically has no boob under her shirt, it's just empty.
It doesn't look like any outfit in the game, as of right now, has a complete body mesh underneath it (although I haven't tested the sweater in the picture because I don't have it yet,) so we either have to wait for an outfit that hopefully does to come in an update, or we have to unpack the files and change them directly.
And, before someone asks, no, the file unpacker in the tools section of the forums does not work on this game. This game has a different file structure from GE2RB and GER.