Disclaimer: I own nothing you recognise; you know the drill

Feedback: Much appreciated

AN: After seeing the Flash/Supergirl crossover 'Worlds' Finest' and how it was incorporated into the timeline of the 'Flash' series, the thought occurred to me that we had an excellent opportunity for a couple of other superhero crossovers before Barry manages to get back to his Earth (albeit so long as there's a suitably fast hero available to give him the necessary boost to re-open the rift). With that in mind, I give you this new storyline, as Barry Allen joins the heroes of another Earth to face a literally earth-shattering crisis; hope you like it.

Mercurial

I'm really gonna miss you too, Kara Danvers

It had been a brief friendship, but as Barry Allen began his 'race' with Kara Danvers, AKA 'Supergirl', he realised that he meant that in more ways than the obvious.

It wasn't that he thought he was better than anyone else just because of his powers, but having abilities in a crisis when everybody else was only human gave him a certain sense of responsibility. He enjoyed the chance to fight and train alongside Oliver, but even if his friend had proven that he could handle a rogue speedster during that incident with Rainbow Raider and the final confrontation with Eobard Thawne, Barry felt that he could… relax a bit more when he was up against a metahuman foe with a metahuman ally.

Being the Flash might be an incredible experience, but it could also be a lonely one; having friends offering advice over the radio wasn't the same as having an ally fighting alongside him, someone he knew could handle themselves against the more unconventional threats he had to deal with…

As he pushed himself further, he felt a sharp force in the centre of his back, and once again found himself in the middle of a dimensional breach. Now that he was aware of what was happening, Barry adjusted his perceptions to take in the effect at a slightly slower rate as he ran, registering more of the strange images he'd experienced during his original trip to Earth-Two. He saw a flash of Kara flying, a dark-skinned young archer in green fighting alongside what looked like a grey-haired Oliver, an older man wearing what Barry could only think of as a 'bulky' version of his own suit… a young man in a red jacket and blue T-shirt charging at a massive grey figure with what looked like bone sticking out of its joints… a figure in red and blue facing what looked like a giant humanoid robot rhino… a man walking against fire to approach a blazing red-haired woman… a group of people firing all kinds of energy at a man in some kind of silvery-blue armour amid a ruined city…

As the distortion effect vanished, Barry almost slowed down before he realised that he was over water and facing a city that definitely wasn't Central, Star or National City. Quickly picking up the pace before gravity could take effect, he ran across the water before he could sink, moving past a large four-storeyed glass building before he entered the city.

As he reached the ground and slowed himself down slightly, he noticed a slight strain to maintain his speed, but quickly pushed that aside; Doctor Wells and Caitlin had both confirmed that the tachyon collector wouldn't hurt him or his connection to the Speed Force, so as long as he could keep running he'd be all right. Continuing to run through the city, Barry registered and appreciated his greater control of himself in this state; when he'd run through the last breach he'd grabbed Kara and then lost track, but now he was taking in his surroundings and still maintaining a good pace. He noticed writing on some of the nearby buildings that he thought looked like Chinese, but he was saved from wondering how a breach in America had sent him to China when he noticed a brief blue flash down another street out the corner of his eye.

Zoom?

His blood cold at the mere thought of the twisted speedster on another Earth, Barry adjusted his pace and direction to follow the blue blur, but it didn't take long to realise that this wasn't his Earth-Two adversary. Whoever this speedster was, not only was he not crackling with blue lightning, but he wasn't even wearing a mask, thick grey hair visible on the back of his head over a dark tracksuit-

A blast of red energy suddenly struck Barry in the side, hurling him into the nearest building so quickly even he couldn't adjust for his sudden shift. Barry briefly registered a dark-haired figure in red in the direction that the blast had come from, but then he struck the wall before he could take in any more, darkness taking over his mind before he even had time to yell.