I played his story on hard mode with my brother who was using a lvl 60 Date Masamune .
Its really hard to go solo with Kotaro because he is so weak. But his attacks give him almost invincible and when you unlock his first R2 move (forgot what its called), you can practically stay in the air and spam that attack to pull off safe air combos.
Just be careful not to get surrounded. --- "Joke topic. Sexy ladies don't play video games ~ Orochi_Oni"
He is very poorly built for boss fights, but does an amazing job against grunts and anything else that has no super armor. Just keep getting people into the air and stringing his combos into themselves over and over again. Once you unlock his R1 attack, he becomes a beast, but once you unlock his Shuriken Super Art, he becomes a fearsome opponent. Once again though, boss fights are a pain. It is hard to hit them and you take damage like a chump. He's very rewarding if you figure him out though. Don't forget to dash cancel in the air. It's necessary for getting around quickly and doing some major combos.
Even though his defenses are paper thin, I find him very fun to use. Shuriken Super Art is a Godsend. It can also be used for boss fights. As it has a vacuum effect and they will be sucked into it. For the ones that don't flinch like Tadakatsu or Muneshige, it still works because of the multiple hits. So he's not so bad. Just a bit rough around the beginning. --- "White people love Wayne Brady, because he makes Bryant Gumbel look like Malcolm X."
To the poster above me, considered Shuriken + R1 alternating? =P You won't land at the floor at all throughout the whole fight and only the base commander might be able to hit you once or twice during this fight..... --- Persona 3 Portable. A Social Link a day keeps your troubles away!
For boss fights (barring Muneshige, Tadakatsu and Kanbe, who can't be launched),
Triangle > Air Attacks (don't finish the combo, only up to the part where he swings around) > Air Triangle (the ground shaker) > Triangle again, ad infinitum can take them out nicely, even more beastly when you equip the accessory that increases air attack damage
--- "Lord Odin! The perversion I felt! It's those two!!!" -- Dog Freya, VP2 --
I died a couple of times because of his health a defense, but he is my favorite character so far :D --- To be fair, no one has unlimited patience, and at times this board could come close flustering the Buddha.-geekneck99 Patience is a virtue but I'm a sinner.