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A mobile game spin-off of iDOLM@STER launched in 2014, this time focusing on producing for the male idols of the 315 Productions agency.

The members of Jupiter from iDOLM@STER_2's 961 Productions are included in the roster, with Akizuki Ryou of Dearly_Stars' 876 Productions being added later as part of his own unit.

In March 2015, voices began to be introduced for the idols, starting with the unit DRAMATIC STARS. ST@RTING LINE, a series of music CDs featuring them and other units, also began to be released by Lantis throughout the year.

In December 2015, a Twitter-based poll called the New Idol Discovery Project (新アイドル発掘オーディション) was run to select three new idols from a pool of nine candidates to form a new unit, with the winners being announced a month later. The winners (Amehiko, Koron, and Sora) were later implemented into the game in July 2016 as the idol group Legenders. The other six candidates have not been put into the game as of late.

In February 2017, Bandai Namco announced the development of The_iDOLM@STER_SideM_Live_on_St@ge!, a mobile spinoff. The game serves as a male counterpart to Starlight_Stage, as it is a rhythm game utilizing 3D models of the 315 idols for in-game performances. They also announced a SideM anime adaptation, with further details being revealed on "315 Day" (March 15). The anime premiered in the fall of 2017.

In 2021, a third game, THE_iDOLM@STER_SideM_GROWING_STARS, was announced following the closure of LIVE ON ST@GE!.