Kappa no Yomeiri

On his way to work at his flower shop, Ryuuto came across Kikujirou who had collapsed on the side of the road due to heatstroke. After his recuperation, Kikujirou suddenly proposes to Ryuuto! It seems Kikujirou is actually a Kappa, and it is his family's tradition to marry the man who saved his life.

(Source: Gentosha Comics, translated)