Newt and Percy knew each other since childhood. I just need utter fluff and teenager antics. Ilvermorny probably has a prom, and Percy asks Newt out.

+ Newt immediately rushes to America because Percy didn't send his weekly owl or didn't show up to their weekly firecall
+ he sees Grindelgraves and figures something is up when he doesn't get a kiss
+ he then rescues Percy (it's up to you how he does it)