What Did You Eat Yesterday? 19

Shiro is the managing partner at a law firm, and he de-stresses every day after work by cooking with his live-in boyfriend Kenji. They've been together for almost two decades now, and while they're no longer as lovey-dovey as they used to be (they're in their late fifties, after all), their relationship is nothing but peaceful. But what happens when the two of them suddenly bump into Kenji's ex, who just so happens to be a buff and handsome-looking guy?