I'm not participating in this giveaway contest (I keep hope to win, sooner or later, in the regular trivia contest), but I'd like to share a crossover idea.
Probably none of you know this comics series, but there is a french comic book about a wolf, a fox and a rabbit having adventures in the Europe of the 17th century (beside the 3 main characters, the world is otherwise populated by normal humans).
The comic book is called "De Cape et de Crocs", and a crossover between Usagi and the rabbit swordman (called Eusèbe, a former musketeer) from this comic series would be great.
The comics is full of word plays and references to classic french litterature and theatre (like Molière plays), so I guess it's quite unlikely to see an english publication, unfortunately.
I may even ask for a commission of an imaginary meeting between the two rabbits, one day, by either Stan Sakai or Jean-Luc Masbou (the french artist).

