Let me name all my username origins, starting with my main.
Pikataro ~ Well, know how Gold from PokeSpecial used "-taro" as a suffix for all his Pokemon's nicknames? Combine "Pikachu" with it, and whaddaya get?
Serene ~ Totally from Riviera.
Zuzu ~ Ruby's Mudkip in PokeSpecial.
Yuyuko ~ The sixth boss in Touhou 7/PCB, as well as a recurring character in plenty of the future games.
Natsu-kun ~ Because "Natsu" was taken, and I have a Fairy Tail obsession, so yeah.
Fia ~ Once again, Riviera.
Suika Ibuki ~ Only new character in Touhou 7.5/IaMP, and she appears in later games.
Lucent ~ I once had a dream, and there was this sexy wizard guy (anime-style, obviously) named "Lucent" (I had no clue where the name came from). Basically, he told everyone they had five minutes to kill him, and when those five minutes were up, he killed them. He took pity on my character, but then when my character tried to revolt he told her the same thing. Long story short, she ended up just waiting for him to kill him, told him so, and he ended up sparing her. Plus, it's a cool-sounding word, no?
Kagebouzu ~ Japanese for "Shuppet", one of my fave first-stage Pokemon.
Yggdra ~ The main protagonist for Yggdra Union.
Sanae ~ The fifth boss of Touhou 10/MoF plus appearing in later games, the Designer/whatever they're called from TWEWY, the mother of Nagisa in Clannad... This can go on, honestly.
Nitori ~ The third boss of Touhou 10/MoF, and she makes her presence known in Touhou 11/SA.
Youmu ~ The fifth boss of Touhou 7/PCB, and she definitely appears in other games afterwards.
Rosary ~ A lovely witch from Yggdra Union; she either dies or joins your team.
Milanor-kun ~ Because "Milanor" was taken, and I love Yggdra Union <3
Lachryma ~ It sounds cool, no? :> Kind derived from Lacrima, which makes an appearance in Riviera as well as Fairy Tail (though it has more importance in the latter).
Lucy ~ Because I love Lucy from Fairy Tail (that was not meant to be a pun, really).
Fairy Tail ~ Um... Explanatory username is explanatory.
Pamela ~ Another witch from Yggdra Union.
... That's it, minus my main's new name once they get it.