Hand reading fails me. What does this donk-barrel-call-donk line rep?

1/3, 9 handed, $500 max buy-in, Parx Philly Friday night. Rake is 10% up to $5 with $2 promo drop.

PRE -

EP limps (UTG or UTG1). He's starting out around $645-ish.

This is the main V. He's white, maybe mid 20's, just sat down with around $300-$400 maybe 2-3 orbits ago. Never seen him before this, so most likely not a reg, or at least not in this room. He won a big pot not long after he sat down, either with a big bluff that got through or hero calling a big bluff that didn't. As I'm typing this, I can't remember for sure which it was.

Too soon to assign him a detailed read with any confidence, aside from saying he appears capable of either running a big bluff or hero-calling a big bluff, and isn't scared money, but otherwise probably isn't very good when he's open limping from EP.

Hero raises to $20 with A5dd in MP. Hero is MAWG running over the table with around $2k in front of him. Should have a winning image. Haven't shown any bluffs since V sat down. Have shown a lot of winning hands, even when opponents folded, so the rest of the table may think I'm on a heater and just always have it.

Two calls from loose-passive rec-fish in LP, folds back to V, who also calls. Four to the flop with ~$80 in the pot.

FLOP ($80) 843rb with one diamond, giving us one over, backdoor flush and inside straight draw.

V donks for $25. Hero calls. Other two fold. HU going to the turn.

TURN ($130) 843rb Ks, completing the rainbow of suits. No more BDFD, just the one over and an ISSD.

V bets again, for $45. Hero decides V is almost certainly FOS when he continues to barrel here, but for such a small size, and we can rep a lot of KX as the PFR, so we raise to $125 (not going too big, just in case he isn't actually FOS). V thinks for maybe 5 seconds, then calls.

Assuming V will check in flow on the river, hero is planning on jamming on any Q, J, T, 6, 4 or 3, sizing down for value on an ace or 2, and giving up / checking back on a K, 8, 9, or 7.

RIVER ($380) 843rb Ks 5c, giving hero 3rd pair.

Hero forgot to have a plan for what to do on a 5, but it doesn't matter. V doesn't think more than a few seconds before stacking up some chips and donking for $225, leaving himself about $250 behind.

I can't remember if I've ever seen this line, and in game, I was very surprised. He donked the river for half his remaining stack, but it's just under 60% pot. Like, what is this line repping?

As hero is tanking, he looks over and notices that V is staring intensely at him, apparently trying to look confident / strong, usually a fairly reliable tell indicating weakness.

I didn't think he'd have a flopped set or 2P when he bets small and then just flat calls my raise on the turn Ks. I wouldn't think 8x would continue to barrel on the Ks turn AND flat call my raise AND donk the river on a brick.

The 5 on the river doesn't change anything, if we discount either of us having some sort of inside-straight draw (76? A2?) that gets there, or somehow arrives on the river with 85 or 54 (just 1 combo each of 54s and 85s). Are 76, A2, 85 and 54 taking this line - donk flop, barrel-call turn, donk river?

Maybe he started a semi-bluff on the flop with 65. But does anyone in his spot river 3rd pair and suddenly decide to turn it into a bluff by donking for 60% pot (1/2 remaining stack)? Without thinking more than a few seconds?

I'm guessing most here will say this is a trivial fold. Maybe it is. But I was having a very hard time putting V on a hand that made sense for value. To be fair, I was also having a hard time figuring out what his bluffs would be.

We beat 65 and worse 5x, like 52 (both open-ended on the flop). We beat hands like A4 and A3 with BDFD's, if he's donking out with bottom or middle pair + BDFD on the flop. And we beat all his random air-balls that are just spazzing. I figure he's got 2 combos of 65s, 2 of 52s, 2 of A4s, and 2 of A3s, so 8 value-bluffs, and maybe some weird air.

We lose to 8x and better. I figure he's got 3 combos of 98s, 3 of 87s, and 3 of A8s - 9 total. If we want to give him 85s and 54s, that's another 2 combos, for 11 total. Do we want to give him 76 and A2?

We're being laid 2.7 to one on a call.

What should hero do?