I'm actually having trouble narrowing down a pick because when it comes down to it, most ninjas in games are characterised by being aloof and looking cool and it's not the trope I gravitate towards.I love how OP also asked "and why?" yet no one really replies to that part, because the answer is basically always just "because he/she/they looks cool"
But I learnt new lore about shadow from FF6 thanks to this thread so yay for explanations.