Ijiwaru Osananajimi to Toroama Fuufu Seikatsu: Kono Keiyaku Kon wa, Kekikakuteki Dekiai deshita

"I've imagined it so many times, holding you in my arms." His pent-up desires turn into passionate caresses.. He loves her so deeply it sends shivers down her spine..! Mizu, an office lady, is suddenly proposed to by her childhood friend, Hiro!! She and Hiro have been together from kindergarten to their first jobs, and have even shared an apartment since university, making them like siblings. Completely swayed by their mutual interests, and despite the warnings of their friend Kamiya, who was drinking with them, they become a couple on a whim! However, it turns out that this wasn't a spur-of-the-moment proposal at all, but rather a scheme by Hiro, who had been eyeing an opportunity to win Mizu over..!? A love story of unwavering devotion from a childhood friend that begins with a zero-day marriage♪ (Source: Bunkasha, translated)