When he first arrived in Aather he didn't remember his name. It bothered him a bit at first because it drove home the fact that he didn't know who he was, and that didn't sit well with him. But anyway as is common in Aather everyone he talked to told him he'd need a temporary one until he remembered his own. He had a couple of suggestions but they weren't things he cared for. KK suggested "Ninja" and he was like "....no" because while he remembered he's a ninja, it seemed like a silly thing to name himself and he knew he wasn't the only ninja in aather, anyway. And when he refused it she agreed and said something to the effect that ninjas wouldn't announce themselves like that anyway. Which made him think like "yes, I guess they'd be stealthier than that" And then it was like "Oh, Stealth could work." So he went with it. And he does consider it a name given to him by his team because a teammate inspired it, so.

And while he has since remembered his real name, he has sort of a complicated relationship with it and doesn't like to introduce himself with it, so he continues to use Stealth. It's not really because he's rejected his past self or anything like that (because he hasn't, exactly), but "Itachi" means something different to him than "Stealth." The only person he has told to call him Itachi is Vincent and that is specifically because he kind of loathes Vincent and doesn't like him using Emerald's name for him. It also reminds Itachi to stay on his guard around him and is kind of a subtle threat toward Vincent.

What kind of games are you looking forward to Sakura playing in?