Perfect Propose

Hiro's so stressed out at work that he can barely have proper meals or get some well-earned sleep. When he passes out on the sidewalk after yet another stressful day, an unfamiliar face calls out to him—apparently, they once promised to marry each other? What's Kai Fukaya's deal, and why is he so insistent on assuming the role of Hiro's fiancé?
(Source: Manga Planet)
Note: The chapter count includes an extra chapter.