Well... first I trained myself dizzy in the Mondwal-Parcours and got the best equipment you can get before defeating Inner Chaos.
I used Sturm und Drang, Close to you, Gaia-Ring, Heroes Soul, Center of the World, until the bitter end, heroes seal, "Schnelles Schwertziehen" - umm.... Quick Draw?, through the wall, "letzter Trotz" - umm... last defiance
and
Omega
won with 140 hp left
winning against Chaos was all about evading his attacks respectively using Ex-Mode to rescue yourself if you got hit."Quick Draw" rescued me by breaking Chaos instantly. By keeping Chaos in Break he also had difficulties damaging me. Well I got Hp-dmg twice and lost nearly when he used scarlet rain. Thanks to Tidus Evasion-Moves I survived the attack without taking damage... ooh... and I had a lot of luck