Hints:

Unlock Burning Batsu:
     In  story mode select Taiyo Gakuen. Now you have to intentionally
lose  a  round  with Batsu to Akira, Yurika, or Zaki. Then Iincyo will
replace Batsu after the match. Burning Batsu will appear when fighting
Vatsu.

Unlock Powered Akira:
     In  story  mode  select  Seijyun Syogakuen. Now defeat Wild Daigo
without using any team up techniques.

Unlock Roy Bromwell and Tiffany Rose:
     To  unlock these you have to successfully complete the story mode
with the Pacific High School.

Unlock Vatsu:
     To  unlock Vatsu you have to successfully complete the story mode
with Gorin Koukou.

Unlock Wild Daigo:
     To  unlock Wild Daigo you have to successfully complete the story
mode with Gedo Koukou.

Unlock Hyo Imawano and Dark Side Student Council:
     To  unlock these you have to successfully complete the story mode
with all the normal schools.

Unlock Kurow:
     To  unlock Kurow you have to successfully complete the story mode
with the Dark Side Student Council.

Unlock Demon Hyo:
     To  unlock  Demon Hyo you have to successfully complete the story
mode with all schools and endings.