That's a really solid build, playing to Sephiroth's strength, which is his overwhelming brave game. Playing conservatively is best, because while he's aggressive with bravery attacks, his HP attacks can be a bit hard to land, especially since he doesn't have a BRV->HP chain.
I think you should probably discard Concentration in favor of a more offensive ability like "Snooze and Lose." That ability is one of the best abilities in the game, which punishes defensive players and forces them to either attack blindly and make mistakes, or have their brave drain away to zero. With an aggro build like yours, and a strategic play style, you can really smash face against opponents with ease.
I'd get rid of Magic and Physical Shield too, because you really shouldn't rely on them to save you. Your own skill and tactics should compensate, and you shouldn't be getting hit that much where you need their buffs. Put those points towards Snooze and Lose.
I'll share my build one day, but its kinda similar to yours. Except my accessories focus more on keeping him in EX mode more than you.