I'm thinking Suya has control over all forms of water.

_____
Beast Shifting for Jayco

Tatsuya : What do you want then?
Garvin: Er… something work related.
Tatsuya : What department is this?
Garvin: Sorry?
Tatsuya : Well, if it’s work related you’d obviously know what department this is. What department is this?
Tatsuya : *looks at Jayco and Brosc* Some sort of homosexual department?

Their relationship in a nutshell

_______
Brosc: Hey, I say we go down there, kick Garvin’s door in, and let them know that we’re in town.
Jayco: That ain’t the way we do things here. We may have to go in there and run a con, drop a bug, do the smooth talking.
Brosc: Okay, you come with me, you do the smooth talking, let’s go.
Jayco: No, we just can’t go in there and kick down Garvin’s door. We need a plan.
Brosc: Well who makes the plans?
Jayco: Tatsuya .
Brosc: Tatsuya , what's the plan?
Tatsuya :You guys are gonna go down there, kick Garvin’s door in, let them know you’re in town.

Garvins' power is something I call Catecholamine Rush. It's a very fun power where he can boost levels of the different Catecholamines. It doesn't actually produce more of it, but it'll use what one already has and then create fake versions of it that are much more potent in how addictive they are. He can use it on others and himself. Usually, it requires a sort of trigger for him to use it. Like, he has to start producing Catecholamines himself the normal way before he can actually use it on anyone.

Garvin: ARE YOU-
Tatsuya : Fucking.
Garvin: KIDDING ME?! YOU-
Tatsuya : Fucking.
Garvin: IDIOT!
Jayco: …What was that?
Tatsuya : Brosc banned Garvin from swearing, so I’m helping them out.

1. Beast Shifting

2. Trickster Lord

3. Lucky Streak

---

The three powers I can give to Jayco

Beast Shifting has my vote .

But the other two sound interesting

Jayco, writing in a letter: "I'm going to kick.. your... ass."
Jayco: THERE. Now send it.
Garvin:: Dude, your handwriting's terrible, are you sure you want to-
Jayco: JUST DO IT!
later
Brosc: So what does it say?
Tatsuya , reading the letter: They say they're going to "lick my...."
Brosc:
Tatsuya :
Brosc: Gross-

Brosc, spraying a melted cutting board with a tiny water gun: We gotta cool this bitch down. Cool it down.
Jayco: I actually just put the cutting board in the oven...
Garvin, visibly confused: Okay, so they decided to put the cutting board in the oven?
Brosc, spraying Jayco: You FUCKING DUMBASS!
Jayco: Dude, I forgot-
Brosc: OH MY FUCKING GOD! We're trying to make Chicken Alfredo right now, and you fucking MELT the cutting board in the oven at 400 DEGREES FAHRENHEIT!?
Tatsuya : *Watching in complete confusion while trying to process this whole situation.*

I vote either beast or luck streak because luck streak could be so useful