Mega Milk seems like it should be a copyright tag, rather than a character tag. It's just a shirt with a couple words on it, after all.

pulsethegryphon said:
It's just a shirt with a couple words on it, after all.

Maybe there's the implication that the shirt is the character, where it is a sentient piece of clothing that has possessed its wearer. Once the shirt it on, that character is now referred to as Mr. or Mrs. Mega Milk, respectively, until the shirt is removed.

Or something. Tbh I don't really know much about hentai lore.