While running trying to stop Godspeed, Grey was trying to get infront of him as Barry stayed behind, but he went to fast and got lost in the multiverse. The breach that opened wasn't blue though, but crimson red. Barry stopped as Godspeed got away.  The breach closed to never be opened again. (This takes place in Season 5 of the Flash, or after thinker) Grey was floating to a Earth not seen before, gavin been knocked unconscious from entering, his body became a anime style and he was shot out in a certain club room. 

[Rias POV]

As we were having our usual club meeting, a portal opened infront of the door. Everyone was getting ready for a fight, but they only saw a unconsious body shoot out of the portal and hit Issei at Mach speed. 

"Ow! That felt like Koneko punching my hole body at once!" Issei said as he got up. He heard a thud and looked down to see a teen boy with a grey and red suit(picture below)

Rias was watching seeing if he was dead and all I've a sodden she sinced a powerful force coming from the male. She then felt his heart stop, she rushed with her rook piece. She reserected him. 

[Timeskip to next day] 

As I was waiting for my new piece to wake up, Issei told me about a nun he met, I scolded him and he left angerly, I heard a moan coming from my room and I saw the male waking up. I sat beside him and put his head in my lap. "Good Morning, Did you sleep well?" 

???: What happened? 

Rias: Well, you came flying out of a portal but died, so I brought you back. 

This hit him like a hurricane, he died but is now alive? WHAT?

???: Excuse me but, how?

Rias: Well, you see, I'm a devil, and you are now too.

???: Oh, well that doesn't make any since at all. Oh, I didnt get your name. I'm Grey!

Rias: Nice to meet you Grey, my name is Rias Gremory. Now, I sensed a powerful force inside you, care to explain?

[Grey POV]

This Rias girl can since the speedforce. How, what, who, when? I debated with myself over weather or not to tell her. 

Grey: Well, you see, I'm from another Earth, Earth 1 to be exact. There I am something called a meta-human. 

Rias: Meta-Human, so what, do you have powers or something?

Grey: Yes, actually. I have access to something called the SpeedForce. I'm actually a hero on my Earth. I was called Vortex, partner of the Flash.

Rias: Well, can I see you uses this power of yours. 

So I brought her into FlashTime. She was astounded, and she essentially affected, I guess since she is a devil and all. 

Grey: Welcome to FlashTime. You are moving as fast as I am. I can move around 50,000mph if I really try.

Rias: Wow! This is amazing! 

Grey: Yeah! Also, with more training I can go faster. 

Rias then had a devious smile, she was up to something. 

Rias: I'm going to have  a training room built onto this but I have one thing to ask, do you need a place to live?

Grey: I think I can find something, I do need money though. 

Rias gave me 10,000,00 yen, which I was shocked about. I thanked her and rushed away to find an apartment, get some clothes. Some food, and sign up for Kouh Academy. Tomorrow is my first day.