Koi Harmony Slot by Playtech

Every koi is chopped into three pieces, head, body and tail, and each reel holds one piece. So a spin doesn't really drop symbols, it assembles one long fish across the three panels, and you win when all three segments come up the same colour. A whole koi in a single shade pays: Purple 20x, Green 40x, Red 60x, Gold 100x, and a Rainbow koi at the top for 888x total bet. There's also a Mixed payout of 8x for a complete fish shape stitched together from clashing colours, the consolation when the body lines up but the palette doesn't.

The Rainbow Fish does two jobs. It's the wild, and it's the top koi. Land a win with one or more rainbow segments in it and a single Respin fires: every part on the board repaints itself one colour, Purple, Green, Red, Gold or Rainbow, so you're guaranteed a complete same-colour catch that pays at the matching prize. That's it. One respin, no retrigger, same stake. No free spins, no jackpots, no buy button, no ante bet. The whole game is that one koi ladder and the occasional rainbow repaint.

The setting matches the restraint. You're looking straight down into a still koi pond, turquoise water rippling over pale pebbles with green lily pads drifting in at the corners, the reels sitting inside a single gold Chinese-style window with the six koi and their multipliers lined up along the top.