2nd pair, weak kicker facing river bet

888 Poker - $0.02 NL (6 max) - Holdem - 6 players
Hand converted by PokerTracker 4

UTG: 94.5 BB
MP: 117 BB (VPIP: 23.75, PFR: 17.50, 3Bet Preflop: 6.67, Hands: 81)
CO: 67.5 BB
BTN: 115 BB (VPIP: 18.52, PFR: 14.81, 3Bet Preflop: 16.67, Hands: 27)
SB: 102.5 BB
Hero (BB): 100 BB

SB posts SB 0.5 BB, Hero posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has Q♣ 7♦

fold, fold, CO calls 1 BB, fold, SB calls 0.5 BB, Hero checks

Flop: (3 BB, 3 players) K♣ Q♥ 9♦
SB checks, Hero checks, CO bets 1.5 BB, fold, Hero calls 1.5 BB

Not the best of flops for my hand but I hit so decide to call the 1/2 pot bet and re-evaluate on the turn.

Turn: (6 BB, 2 players) K♦
Hero checks, CO bets 4 BB, Hero calls 4 BB

Ok, so the 2nd K makes it less likely that he has a K and I still have 2nd pair so I call again. I could raise but don't want to build a pot with a weak hand.

River: (14 BB, 2 players) 5♥
Hero checks, CO bets 9 BB, Hero ?

The river seems to be a blank. I hope he checks so I can check back with some showdown value but he bets again. I have zero hands on this player so no help there. I was stuck on this one, the fold seems to be a weak but obvious choice facing his aggression and a raise seems ott for my hand and basically means turning it into a bluff. I was 90% certain he did not have a king but that 10% was bothering me.
I finally called. If I'm honest it was as much to see what he had as anything. Not the best reason for a call but at least I had a reason.

Any thoughts are appreciated.