Nostalgia: Op.2 (Op.2 meaning the second opus) is a piano based rhythm game in Konami's BEMANI franchise. It is the second game in the Nostalgia series and a spiritual successor to Konami's Keyboardmania series.

The game consists of falling bars corresponding to certain areas of the keyboard. When the bars cross the judgement line it is time to play that key. There are three type of notes - Normal note which you play as normal, slide note where you slide your hand across the keyboard and trill note where you rapidly and alternately press two neighbouring keys.

Op.2 adds a recital mode, with more strict timing, pressure requirements on key presses and bigger penalties on misses and how many keys may be played at the same time. Recital mode also challenges you with picking songs of a certain theme to fill your game session. An enourmous settings screen was also added so that you can customize your play (scroll speed, note style, falling style etc.).

The story mode added proper progression with a map screen, diverging simultaneous stories, and themed worlds with according unlockable songs. All songs from Nostalgia and Nostalgia: Forte are returning for this game. Along with the 126 new songs in Op.2, that brings the total song list up to 307 songs.