Assuming you're correct with Yassun (I agree with you on that one), MIWA and SHA-V are the only aliases in the last two lines for Fatal Fury: Wild Ambition not featured in the earlier six. My money's on SHA-V for 2 reasons:
1. The V in The Last Blade 2 is a big tip off
2. It's the one with an S, a letter that's pretty rare among these names.
As for Samurai Showdown: Warriors' Rage, the two are ASSHY and BERO-OU. I'm going with ASSHY for this one because:
YASSUN (Two Ss in name)
YASUHIRO ---->YASSUHIRO (Assumes Yassun is Yasuhiro; has H in name) -->YASSH (subtract UN; replace with H)
Therefore,
YASSH----->ASSHY by simply moving the Y at the start to the end
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