@NWSiaCB: I've also seen it in original works where there...

NWSiaCB
2014-10-07T10:58:52-04:00

I've also seen it in original works where there are multiple original characters, most of whom don't appear in every page of a given work. (USUALLY, this means it's an entirely original work, rather than just a fanfic, although there are some exceptions.)

I.E. Trouble Spirit has numerous characters, and if you want to search only for panels where Tiko is speaking with Priss, you'd be hard-pressed to find it just looking through the pool. Likewise, Karin-dou has well over a dozen characters, and given how long a character can go without reappearing, having a wiki page for the characters to be a refresher isn't a bad thing.

Touhou Boys and Girls was an extended "if they mated" series that got their own character tags for similar reasons, in spite of being a fan work. Xialing (Meiling and Sakuya's child) appeared all the time, but Iris (Alice and Reisen's child) appeared only rarely.

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On the topic of Matsuda Chiyohiko, I've seen multiple crossover images made by other artists. Kei-Suwabe in particular seems to have his abyssal admiral drawn by other artists, while drawing Matsuda in his occasionally. I.E. post #1752859

Here's some other Chiyohikos by other artists, just looking around randomly:

post #1752338
post #1774442
post #1646211