Villain is fishy - 28/15 only 2.5% 3bet (only 120 hands so far). Sizing is obviously fishy preflop too. Postflop AF are low so generally quite passive, but not as much as some.

I think he shows up with AK here so often that even with the fishy river sizing I wanna fold, anyone disagree?

Poker Stars, $0.10/$0.25 No Limit Hold'em Cash, 6 Players
Poker Tools Powered By Holdem Manager - The Ultimate Poker Software Suite.

BTN: $44.52 (178.1 bb)
SB: $42.73 (170.9 bb)
BB: $29.66 (118.6 bb)
UTG: $41.45 (165.8 bb)
MP: $102.12 (408.5 bb)
Hero (CO): $85.89 (343.6 bb)

Preflop: Hero is CO with K K
UTG raises to $0.50, MP raises to $1.50, Hero raises to $3.25, 4 folds, MP calls $1.75

Flop: ($7.35) 3 6 A (2 players)
MP checks, Hero checks

Turn: ($7.35) 5 (2 players)
MP bets $2, Hero calls $2

River: ($11.35) 3 (2 players)
MP bets $4