Play as Miharu:
Select single player Tokimeki mode and enter Angel as a name.

Play as Rei:
Unlock Miharu, then press Up(2),Down(2), Left, Right, Left, Right, B, A at the "Press Start" screen. Rei will be selectable in all modes except single player Tokimeki mode.

In-game reset:
Hold A + B + C + Start during game play.

Alternate costumes:
Select any mode except single player Tokimeki mode. Highlight a character and press Z, Y, or A at the selection screen. More costumes will appear for a character after you set the Saturn's system date to match that person's birthday.