Bleach: Season 1, Episode 309

1 - 309: Fierce Fighting Conclusion! Release, the Final Getsuga Tenshō!

Battle ensues between Aizen and Ichigo. His nineties-level Kido attack easily deflected, Aizen further evolves to best Ichigo. But Ichigo, now fully aware of why Tensa Zangetsu was reluctant to teach him the Final Getsugatensho, has come to possess amazing powers.