Steps

First, I think you need to at least win 12 grudge matches. Then go to your school, and
then to the clubhouse. Beat your doppelganger and then he will give you a p*** to go the
underground. To get to the underground, go to the house in the southwestern side of Habor
(town left of Midheart). Talk to the guy and he'll open the entrance (stairs) to you.