Mr. Kurosaki's Pure Love Never Stops.

"Please marry me, for one-billion yen." Koharu is a high school girl who likes to cook and help out at her family's restaurant. But Koharu's peaceful life is interrupted by the sudden proposal from Kurosaki, a mysterious regular customer whose face is obscured by his shaggy hair. He is polite and courteous, but his behavior is not quite normal. He just wouldn't take no for an answer. Will his pure-hearted and determined courtship lead to ― a happy marriage!? (Source: Comic Polaris, translated)