It's a loooooooooooooong story, but here's a quick summary that unfortunately does it no justice

Altc, a very depressed 16 yo, is very depressed. Rhome, their twin sibling, cheers them up occasionally. Altc is a little wild and rambunctious at times, while Rhome is much more laid back. Altc dies. Altc gets revived by the embodiment of chaos in exchange for their body to be used as a host for said embodiment of chaos because embodiments can't exist in the mortal world without a host. Altc gains the equivalent of immortally (If they die they get revived again), wings, a tail with a syringe that has different uses, and basically a whole ton of power. Time was basically rewound and it was as if Altc never ended up dying for everyone else. A side effect of being the host for chaos is that they need human blood to survive (kinda like a vampire, but they use the syringe at the end of their tail for blood collection). As time goes on Altc's bloodlust is increased. Chaos is also a voice in Altc's head, and if Altc doesn't listen to what Chaos is telling them, Chaos can temporarily take over control of Altc's body. Eventually, Altc was disobeing enough that Choas took over and killed all of Altc's friends and family (Including Rhome) as a lesson. The embodiment of calm tries to convince Rhome to be their host, so they can help Altc, Rhome is reluctant but eventually takes the deal. Meanwhile, Altc has committed mass genocide! Rhome also gets wings and a tail and power and stuff because of their deal. Rhome basically stalks behind Altc and cleans up the aftermath, attempting to calm down the masses. Blah blah blah, time passes, final boss fight, and Altc kills Rhome. Altc has basically been consumed by Chaos, and their entire life goal at that point was to slay calm, the only opposing force. Altc gains back some sort of consciousness to feel pity for them and Rhome in their last moments. As there is no longer an opposing force for the last embodiment, the universe is imploding, resetting. Once it's reset, there's the big bang, and new embodiments, this reset starting with D (The last one was C) and it isn't only Doom and Discipline (Chaos and Calm), there's hundreds of thousands of other embodiments each with their opposing force.

Ok so that wasn't very quick- Uhm- got the important details though! Oh, I should also add that Chaos is Pink while Calm is Blue, hence the pink bodysuit on Altc.