Monsta X - Dramarama

Plot 1: Hyungwon, the time-traveling maestro, drops a watch off with Minhyuk at the Traveler coffee shop where he works. Minhyuk uses the watch to meet up with his brother I.M, but the men in black find them and try to kill them. Minhyuk returns to his current time & place, but I.M is stuck in a different time and the watch is shattered. Hyungwon, presumably, retrieves and repairs it to give to Kihyun in Plot 3.
Plot 2: Future kendo-lover Wonho goes back to current time to spar with Shownu, even though he knows there's a time-travel crackdown going on. Kendo is sweaty business, so Wonho takes a shower afterwards (thank you, MV!) Unfortunately, the men in black take the watch, keeping him stuck in the future while Shownu waits patiently for his battle buddy to return.
Plot 3: Pawn-shop worker Kihyun can't get over the death of his buddy, Jooheon, in a car crash many years ago. Hyungwon anonymously slips him a time-traveling watch. Kihyun returns to the past and tries to prevent the accident, to no avail. Hyungwon arrives and (presumably) makes a deal with him: swap places with Jooheon in the car, and Jooheon will survive. Sucky deal, Hyungwon. Kihyun takes the offer and now it's Jooheon working glumly in the pawn store with a dead best friend.

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