>>47395133His sync isn't as big as champ iris or marnie when fully set up, but the reason his sync is so good is because setting it up is EXTREMELY efficient. Other techs often don't start to hit huge numbers with sync until the second one because they need to do debuffs and stuff first.
Kukui gets the 1.5x multiplier from dominating sync just from terrify activating at the start of the fight, and then he has the built-in inertia boost on his sync after two uses of his trainer move (each gives +3 speed). Also if you 6*EX him you get another 1.5x multiplier. If you run pecking order then you'll also get another small bonus from terrify (more if you pickup the second terrify node on his grid) and the 66% chance to drop attack on darkest lariat.
So on a team with something like 6*EX masked royal+hilbert+anyone, lets say you do something like:
ready fight/in this together/filler
ready fight/in this together/filler
darkest lariat (procs attack drop)/filler/filler
your first sync now has an effective base power of 240*1.5*1.3*1.5*1.15=807ish
Even champion iris can't setup her first sync nuke this efficiently, even if her sync can theoretically hit far higher numbers.