Haro no Puyo Puyo uses a five-color variation of Tsu rule. There are slight changes to the overall game flow; namely, lateral movement speed is constant when the D-Pad is held left or right (most Puyo Puyo games increase movement speed when the joystick/D-Pad is held), and there is also a notable delay when the player fully offsets Nuisance Puyo. Visually, the game replaces Puyo with the Gundam franchise's iconic mascot, Haro.
The game features single-player, multiplayer, and Endless modes. The single-player mode is an AI gauntlet akin to most Puyo Puyo games, with cutscenes featuring Mobile Suit Gundam's most iconic characters; there are multiple potential scenes for each character matchup that encourage repeated playthroughs. In Endless mode, players attempt to match Puyo until they are defeated while fending off periodic garbage attacks.
The game places a heavy emphasis on "chain phrases," the vocal clips that play when characters make chains. In Haro no Puyo Puyo, each character's phrases are fully customizable, with several phrases unlocking whenever the player clears the single-player mode. The player can also choose to either make the character restart their chain phrases with each new chain sequence (as in most other Puyo Puyo games), or loop. (For example, if the player made a 5-chain, the next chain sequence would start with the 6-chain phrase.)
