Half-Minute Hero, released in Japan as Yūsha 30 (勇者30 Yūsha Sanjū, lit. "Hero 30"), is a hybrid real-time strategy/action RPG/shoot 'em up developed by Marvelous Entertainment for the PlayStation Portable.
Half-Minute Hero's single player mode features 6 different game modes. Each mode is based on one part of a larger story, and as such, the last three modes are not available until the player has completed the first three modes; these last three modes are then unlocked in order after completing the previous mode. Each mode centers around a mechanic based on a limited amount of time (normally 30 seconds as implied by the game's title) to complete that part of the game.
Source: Wikipedia, "Half-Minute Hero," available under the CC-BY-SA License.