Kyoshin Poseidon characters and uniforms:
To unlock Kengo Mizumachi and Shun Kakei, beat Story mode with the Game Boy Advance game Eyeshield 21: Devilbats Devildays in the cartridge slot. To use Kyoshin Poseidon uniforms, hold L while choosing an edit team with Shun and Kengo in it.
NASA Aliens team:
To unlock the NASA Aliens team, beat Story mode, then defeat the NASA Aliens when they challenge you.