Time is relevant. If you know how to wield it

Elemental Mythicals Book 1

The future. The past. It's all relevant. At least, when you can remember it.
I, unfortunately, can't remember anything about my life before three years ago.
Especially not these big men, like this guy Richard, who seems to know me very well. (And ho-boy does he make my motor run).
I might have stayed away and avoided him. At least, until me and my sister needed help.
Now the past I can't remember may be the only way I have to save her.
Because if what they're saying is true, then I'm a time traveler, and I may have to figure it out if I'm going to save my sister.

While a standalone, it does take place in the Mythical Knights/Vampire Mythicals world.