Oswald

In a particular Southern country, many animals are living in the garden of a king's palace. Agifu, a black leopard, is the leader of the pack, and one day he's asked to care for Val, a young white lion. Val's a coward, a cry-baby, and tiny, but under the strong and dashing Agifu, he grows into a fine man while learning to adore Agifu. Each time he yearns for Agifu, he tries to mate with him, but fails. This is the start to a furry love story where both sides can't seem to be with who they want when they go into heat!

(Source: Renta!)

Note: The chapter count includes one extra.