Freaking Obvious Fix 3

Have it that the Masamune clouded Karsh's mind so he thought he attacked Dario. It fed upon his inferiority to think that the only reason Dario attacked him could be in self-defense. His mind filled in the rest.

Lynx was not involved, and if he was, it was tangential-he saw Karsh's memories being edited and in "caring friend" mode manipulated his guilt and fear to ensure he lied while Lynx hid the corrupt Masamune (really, he needed it to guard the Sea of Eden).