Hold Y + L + R + Select at the title screen, release the buttons, then press A.
Azaka and Kamidake:
Take the north route to the spaceship.
Katsuhito is at the hot springs. Go there and defeat all the monsters to add Katsuhito to your team.
You get Mitzuki after defeating Kusumi for the first time.
Ryo-Ohki is in the carrot fields.
To add Sasami to your team, go the south route to the spaceship, go to the prison on the spaceship, or simply continue to the control room. She will be level three for all of these methods, except for if you go to the prison, She will be level four if that is done.
Revisit Mihoshi’s Shuttle to add Yukinojo to your team. She is weak and takes many Kiai units to attack.
There are two routes to get to the spaceship, north and south. The south route will give you Sasami before entering the ship, but you will not be able to get Azaka and Kamidake. Go north for that. The differences between the two routes have nothing to do with monster strength. The south route is fun because the route narrows ultimately to one square wide. The north has more water areas.
Washu is found in the ship’s storage room.
The maximum level that each character can get is 8.