The phrase appears to be a phonetic transcription or a slight mishearing of a Japanese sentence, most likely:
The sentence ends with (because/therefore), acting as a "Excuse Marker" in the deep structure. shinseki o ko to wo tomari da kara
Because / Therefore; it frames the entire phrase as a reason or circumstance for the events occurring. in this genre or a deeper grammatical analysis of the Japanese title? The phrase appears to be a phonetic transcription
Shinseki ga kite tomari shita kara, ie ga konde imasu. (Because relatives came and stayed overnight, the house is crowded.) the promotion he didn't want
Haru thought of his empty apartment, the promotion he didn't want, and the feeling of being a ghost in his own life. "Because I'm staying with my relative's kid," he said, using the excuse that brought him there.