In Season 1, Episode 8 of A Couple of Cuckoos, titled "Are you going to marry him?" (or "Will You Really Get Married Like This?"), the story focuses on Sachi Umino, Nagi's younger sister.
Key Plot Points:
Sachi's Move: After growing suspicious of what is happening between Nagi and Erika, Sachi decides to run away from home. To Erika's delight and Nagi's annoyance, she moves into their household to keep an eye on them.
Investigations: Sachi begins investigating the nature of Nagi and Erika's relationship to "get to the bottom" of their living situation.
Erika's Hidden Agenda: Erika is shown searching for someone on social media, though it is not yet clear if she is looking for a specific individual or someone meeting certain criteria.
