i m not sure what you mean by downloading characters manually...
but its possible to delete all the characters you dont like (simply delete them on the userdata folder.) or adding characters you like.
you can add all the MMD characters and all stuff related to MMD (including moves/dances, chars, items etc..). 99% of them would work, except if they are on textures .dds.
in fact, i noticed that the MMD characters are even better becaue they tend to be rigged way better and have better moves (no weird chickens legs, 360 twist wait etc..)
the nude pack of Dead or alive girls i posted before is by far one of the best rigged one. except a lil' bug with hair physics with chest, their moves is absolutly perfect. (rigged skeleton is amazing)
if you want more chars, have a look at MMD chars (sometime some nude models come up
) , best place to look at is "DeviantArt".. its full of characters (nude or not)
here exemples with One Piece characters
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