because Honoka is Raidou's default partner whenever you go into his challenge mode she's playable for his tag challenge and you even have complete access to her move list since they change it for whatever character you're using at the time. i know their fanbases don't exactly overlap much, but i thought some would like a free try out.
btw this doesn't work the other way because Marie is Honoka's default tag partner.
btw this doesn't work the other way because Marie is Honoka's default tag partner.