[SH] NL50 22 set facing river chRaise

Prima, $0.25/$0.50 No Limit Hold'em Cash, 5 Players

SB: $34.44 (68.9 bb)
BB: $56.72 (113.4 bb)
MP: $75.75 (151.5 bb)
CO: $14.58 (29.2 bb)
Hero (BTN): $144.54 (289.1 bb)

Preflop: Hero is BTN with 2 2
MP raises to $1.50, CO folds, Hero calls $1.50, 2 folds

Flop: ($3.75) K 2 3 (2 players)
MP bets $2, Hero calls $2

Turn: ($7.75) A (2 players)
MP checks, Hero bets $5.50, MP calls $5.50

River: ($18.75) 5 (2 players)
MP checks, Hero bets $13.50, MP raises to $31.50, Hero ???

Anon table.

MP played 23/14 after 120 hands, AFq 45, wtsd 23 so far.

Flop/turn standard I guess, river clear valuebet vs Ax/Kx. But what would you do after his chRaise? It would be a weird bluff from him, and his valuerange is quite narrow in this spot. Potodds are 22%.
I only beat AK, but I'm not sure how many combos to count with (it's pretty sure, that not all of them...). If I take 3 combos out of the possible 9, I dont have the odds to call.

Board: K♥2♣3♦ A♣ 5♥
       Equity     Win     Tie
MP3    80.00%  80.00%   0.00% { KK+, 33, AKs, A4s, AhKd }
BU     20.00%  20.00%   0.00% { 2d2s }