Let's Ride! (Union x FGO x Male Reader x Bionicle)

(Couldn't think of a better title, oh well)
The search is on as Chaldea attempts to find the Seventh Lostbelt. While attempting to track down any signs of the Foreign God, Chaldea sensors pick up a strange anomaly.

In another universe, in another Earth.
An Earth that has an Academy called Union.

Upon arrival, they are met with unexpected outcomes after saving the heroes from a dangerous threat.
(M/N) must deal with the bullies that had hurt his counterpart in that world and track down whatever caught Chaldea eye and attempt to stop the disturbance from affecting their world.

But...threats are everywhere.
And the biggest threats are not from the villains of that world.

But from two powerful beings that threaten to destroy not just that world but the universe itself.
Can the Toa and Chaldea be enough to stop them?
Or will help come in the form of an unexpected Rider?

Disclaimer: I don't own anything except for the plot!