Station Square

First page of the first issue, and he's already too late.

Station Square is a fictional city depicted in the video game Sonic Adventure. In the climax of the game, Station Square is destroyed by Perfect Chaos, who is in turn defeated by Sonic the Hedgehog.

In Sonichu #0, a Pikachu five miles from Station Square notices Perfect Chaos attacking the city, and goes to investigate (at apparently great speed, since he travels the five miles in practically no time). There, a fateful collision with Sonic causes him to be transformed into a new Pokemon with the combined powers of Sonic and Pikachu. The hybrid creature assists Sonic in defeating Perfect Chaos, and returns to the wild, naming himself "Sonichu"

In the Sonichu Chronicles Chris makes clear that this is the fight from the end of Sonic Adventure. He brings this up while paradoxically trying to explain that Sonichu is a Parody of Sonic the Hedgehog, while at the same time making clear that he is an in-universe character that compliments and expands on existing Sonic cannon.