Sweet Fuse is a mystery and romance visual novel in which the player assumes the role of Saki Inafune, as she plays through seven days of death games. Much of its gameplay is spent on reading the story's narrative and dialogue. The player will be prompted on occasion to pick what to make Saki say. Picking the correct responses will sometimes given the player an "affection point" for a particular character which raises that character's affection level. There are moments during which Saki will become irate, indicated by the screen shaking and turning red, and the player will have to choose between having her restrain her anger or letting it out.

"Explosive Insight" sections take place when Saki must find a solution or an answer to a problem. Saki recalls the situation to herself, with a number of keywords and phrases in her thoughts highlighted. The player can pick up to three highlighted words or phrases to select, and the player prompts Saki's epiphany if one of their selections is correct.[1] If the player does not select the correct phrases, a bad ending will usually occur and they are prompted to try again.

The game follows a branching plot line with multiple endings; depending on the decisions that the player makes during the game, the plot will progress in a specific direction.