cross over fan fic

I normally don't indulge in cross over fan fiction, I often think of a scene or two but I give them very little thought (truth be told I'm not much of a fan fic fan in the fist place) but I had a little idea a bit ago I think there are a few interesting dynamics that are worth exploring, and I may try to do this at some point with my own characters in an original setting.

the basic premise is that one of the assassins from assassins creed (I'd prefer altair over etzio but one from the modern age may work best) somehow goes to gotham city and eventually meets batman.  it would probably work best if it started off from batmans point of view and altair's introduction was after batman started examining the death of his targets.  as un batman as it may seem, having batman be unaware of the nature of the assisnation victims until after he'd met altair, not that altair would tell him. this provides some immediate conflict and should give a nice fight/chase scene,  perhaps with some nice dialog at workable points.  after this encounter batman would start digging into the victims and discover what they were really up to and here is were I think most of the story would take place.

I think what I like most about this story is the morals at play, batman may not be the perceived to be as big of a moral paragon as say, superman. but he still lives by a very strict unbending ethical code, most notably not killing people, and while the assassins do kill people, they seem to have a small tinge of regret about it and very strict rules not to kill the innocent (even if players like to violate this rule themselves).  so contrasting the assassins willingness to kill hundreds to improve the lives of millions or billions, would make a great contrast with batmans strict moral code that sometimes ends up in civilians suffering (how many people have suffered because the joker escapes).  you also might be able to explore some interesting possibilities with how much effort batman puts into pursuing the assassin since he only kills these bad people and batman presumably has other criminals and supervillians he could pursue.

unfortunately I'm not too familiar with batmans character (watched the old cartoon show, talk with a lot of people who read his comics but I haven't read them myself) to fully explore batmans reaction to it, one of the major reasons I think I want to do something like this with my own characters, but with my own characters I have the problem of trying to establish how strict the moral codes of both characters are, without bogging down the story.