Gouman to Zenryou

Nishizawa Kakeru is engaged to his fiancee, Sakaniwa Mami. After he was dumped by his long-time girlfriend, he looked for a woman he could marry and he met Mami through a dating app. She is modest and witty, but after a year of dating, they are still unmarried. One day, Mami tells him that she is being stalked. She then disappears. Kakeru tries to find clues that can lead to Mami's whereabouts, but he faces the truth about Mami's past.

(Source: AsianWiki)