historically speaking, ninjas had little to do with fighting, if they could avoid it, theyd get intelligence, spy and if caught and had a way out, theyd escape, so by that definition 'coward' compared to samurai is fitting, but it was all about smarts. Thats why they had blinding powder and incorporated cheapshots into their techniques. They also had no problem with gunpowder or explosives, and during the later part of the segoku period, Date Masamune started incorporating firearms into his army. It wasnt about morals, it was about winning, his spies also did the same if they could as far as can be understood.
If you want a better idea of ninjas than simply what hollywood or pop culture churns out, read the translation of the Ninpiden and anything by the historical ninjutsu research team. It's fascinating.
Do you know anything about ninjas? In real life they used worst stuff then guns and they are all about ending a fight quickly. I'm pretty sure Ninjas would have used a silenced handgun if they were around at the time. They used gunpowder and made bombs. If you are talking about Ninja turtles 1.bp.blogspot.com/-N1c1gr2K7S4…
Imagine them making a game that took inspiration from you. Him using a silenced SMG, and the turtles occasionally killing some of the more brutal villains (preferably not human). I mean, the game should still be rated T, and not have blood, but remind you Vice City and Arkham. If the characters upgraded over time and became more different. Raph using guns and that armor from the CG movie. (and the chains).
They only need to look to Deviant art to find inspiration for different evolutions and gear.