All Square Enix needs to do is play the first bit of the One Winged Angel theme and they've already hooked thousands of Sephiroth fans.
For his next trick he'll appear in Mobius Final Fantasy, theme and all, until March 31. Basically all you need to do is select a specific encounter and you'll be temporarily changed into a playable Sephiroth. The game is also getting a new job, the "Flower Girl of Midgar," a clear Aerith/Aeris reference.
He follows a series of crossovers going back to 2017 for Mobius, which already hosted Cloud (and Sephiroth for that matter in another form), and Tidus. As a reminder Mobius Final Fantasy was released in 2015 on mobile devices and 2016 on PC. It's a free-to-play game that's garnered a mixed reaction due to its microtransactions.
via destructoid https://www.destructoid.com/sephiroth-is-making-an-appearance-in-mobius-final-fantasy-because-he-s-sephiroth-and-can-crossover-whenever-he-pleases-485918.phtml