*This opens with the distant past; Classic Sonic is running through Green Hill until he hears a noise and senses a brief earthquake, though he ignores it. Soon after though, a mysterious entity known as the Time Eater appears in the sky and everything whites out.

In the present day, Tails arrives at a gathering that is attended by his friends. Arriving soon after, Modern Sonic discovers that his friends have been preparing a surprise birthday party for him, as it is his birthday.

Modern Sonic celebrates his birthday with his friends until the Time Eater disrupts the party by sucking everyone through various Time Holes and scattering them across time and space. Not happy with this, Modern Sonic tries to attack the monster, only for it to knock him down. The impact of the attack leaves Modern Sonic unconscious in the grass.*

*Meanwhile This other part is directly preceded by the web series Sonic X Shadow Generations: Dark Beginnings. During Sonic's birthday party, Rouge calls Shadow to ask him if he is still aboard the ARK, and if he will make it to the party.

Shadow declines, explaining that G.U.N has detected an abnormal bio-sign on the ARK and that he will not leave until he eliminates any possible threat, suspecting the return of the Black Arms. He soon discovers that the source is indeed Doom's Eye, and gives chase through the Space Colony ARK. Suddenly, he is pulled into a distorted Radical Highway called the Doom Zone, and receives an odd token by hitting Doom's Eye before returning to the ARK. After Shadow collects the fake Chaos Emerald which Tails once used to trick Eggman during the Space Colony ARK incident, the Time Eater appears and drags Shadow into White Space.

In White Space, Shadow notices a large Black Arms satellite, the Black Moon, hovering in the air. He quickly meets E-123 Omega, who was tracking the Time Eater before he was pulled into White Space too.*