Well, I might have played the original Cytus before although I didn't have so much time to play the heck out of it although it had tons of songs to go through and the challenge is quite equal to the challenge level from the arcade rhythm games. The original had been updated with tons of chapters and needless to say, the story doesn't end there when the sequel had recently come out a few months ago. The story of the original Cytus is that some mutant virus or whatever has taken place and to find a safe place for humans' survival is a tough thing, not to mention that the human memories have to be archived or something. There lies an Android that needs tons of memories through music so I don't know what happens next in the sequel. I also know the story of Deemo as well and it's quite dramatic.
Before the sequel hit the final stage, it was available on IOS in beta stage. And at the time, Rayark is also working on the Playstation 4 version of Deemo which is a strange move to me as it may borrow the strange move from the Switch version of Voez in which you use the physical controls when compared to the touch screen controls. I don't know if that defeats the challenge but such games like Deemo, Cytus and Voez should stay on the devices that are touch-screen compatible. To port a mobile rhythm game to console with full control compatibility like Musync on consoles is a different story.
Prior to regular updates of the original Cytus, you have to pay for additional chapters but as the game became popular, it was updated for free with additional chapters unlocked without having to pay for them. Perhaps, it was to combat piracy or something but what about the mods and hacks that make the game unfair?
The song, Brain Power, is a famous one. It was originally on Sound Voltex II before the DJ/producer ended the contract with Konami to ensure that he had the full rights to the song. Eventually, it was available on other rhythm games as a third-party song including Cytus II. You can check out the story if you want but be warned of spoilers.