This game is titled Tokobot in North America and Europe, and Karakuri in Japan.
Successfully complete the game to unlock the bonus
game center and time trial mode.
Kill monsters to get Tokobot parts in an area with a door nearby. Exit through the door, then return to the previous area. The monsters will have respawned, and can be killed again for more Tokobot Parts. Repeat this as many times as desired.
Strategy guides from GameFAQs