So the phrase is more than a simple statement; it hints at a between the narrator and the embodiment of future possibilities.

親戚 (shinseki) in Japanese means "relatives" or "extended family." It refers to family members beyond the immediate nuclear family, MailMate.jp Shinseki No Ko To O Tomari Da Kara Eng Better High Quality

A narrative centering on the dynamics between family members or relatives during a temporary stay or visit.

If this is the title of a manga or anime episode (which is the most common usage for phrases like this), the localization should highlight the premise.

Shinseki no Ko to Otomari Dakara (親戚の子とお泊まりだから)