Play through the game (beat ''Final Stage'') and save the game. From now on Professor K from Jet Set Radio can be chosen as a playable character. He is located between Garam and Beat on the character selection screen (you can't see him dancing like the other characters, only his picture appears).

Beat all Kogane-Cho levels with a Jet ranking

Get a Jet ranking on all Benten-Cho levels.

Get a Jet ranking on all Shibuya-Cho levels.

Repeatedly tap (A) after turning on the game. When the Sega logo appears, you will hear the trademark "Sega!" scream instead of the short jingle.