Cytus Alpha

The gameplay of Cytus relies on Active Scan Line, which moves up and down across the screen. The player must tap circular objects, known as Notes, as the Active Scan Line passes over them, following the music. Different types of notes are used: Click Note (a single circular note, that requires tapping the object in time), Drag Note (a continuous track of notes, that requires dragging along the track), and Hold Note (has an extended ribbon meter, requires the note to be held until the meter is filled).

The notes to be hit as the line rises are colored blue and purple (light green in Cytus II), while those as the line falls are colored yellow and green (light blue in Cytus II). Each note provides a score based on its accuracy, which can be "Perfect", "Good", "Bad" or "Miss!". Hitting consecutive notes in a row with either a "Good" or "Perfect" rating will result in a combo, which provides a score boost that increases as the combo rises. At the end of a song, the player is given a score out of 1,000,000, with a minimum of 700,000 required to clear it. The player also receives a letter grade: "Fail" if a song isn't cleared, C at 700,000 points, B at 800,000 points, A at 900,000 points, S at 950,000 points, and Million Master at the maximum 1,000,000.

The story of Cytus is carried through its 10 main chapters as well as a prologue. The story is told in-game through various cutscenes that are unique to the chapter title songs; individual songs within each chapter are at most only marginally relevant to the plot, except for a limited few. The plot features the disaster and the protagonist's struggle with identity.

The story revolves around the protagonist, Vanessa, who lives in a 22nd-century world where robots with human memories are the only things remaining while the other living humans are killed by a mutant alien virus that came from outer space. Later, she determined that she was one of person who entered memory transfer services powered by ExtenLife to extend their life and live with her loved ones. The transfer is interrupted due to limited memory space and her emotions are corrupted. As human emotions are stored in the form of music in "Cytus"; by playing the songs, the robots can revive their human emotions.

As of April 2021, Cytus ranks #8 in the iOS App Store's "Music" category in the United States.

Smartphone game reviewer TouchArcade gave the game 4 stars out of 5, saying that "the gameplay is pretty simple, but well executed", though noting it lacked a health system and had fairly loose hit detection.