Sachi is out visiting her folks at the newly opened family diner, so when a storm causes a blackout, it’s just Nagi and Erika, who instinctually hold one another. Growing up loaded, Erika is so unaccustomed to outages she assumes the Martians are attacking.
Once she lights her aromatherapy candle, she and Nagi calm down, and have a cozy little conversation about how much fun they’re both having. Then Erika realizes there’s an emergency kit in the entry hall coat closet and has him go collect it.
While in the hall, Nagi finds a puddle, then trips and falls into who he thinks is Erika…but it’s actually Sachi, who just got home. When he falls into her, they lock lips, but he dismisses it as no big deal and returns to Erika, who is calling for him like a wife would.
But it is a big deal for Sachi, and there’s no way she can forget it! After hearing the exact same scenario play out on her and her friends’ favorite anime, she decides “Screw Onii” and avoids him for the next couple days, making the atmosphere at home awkward for everyone, including Erika.
When Nagi finally comes clean to Erika about what happened, Erika dons her sexy teacher cosplay and points out where Nagi erred. He may still see her as his brat of a kid sister, she’s close to marriageable age; a “proper woman”, and Nagi was insensitive.
When it’s just Nagi and Hiro at the next library study session, Hiro can tell something’s up and offers her services as spiritual counselor free of charge. She tells Nagi he can be insensitive, especially when he blew through her admitting she was engaged and publicly declared academic war against her. But she also likes how straightforward and direct he is, so she advises him to be that way here.
Thanks to the perspective and advice of two other people who care about both him and Sachi, Nagi arrives at Sachi’s door nervous but prepared to end this little row with honesty and contriteness.
He tells Sachi he’s sorry for hurting her and being so thoughtless, and declares his intention to no longer look at her or treat her as just his kid sister, but the proper woman she is fast becoming.
His words do the trick; we know that Sachi wanted this from Nagi, and hearing the words from his mouth without her having to beat him over the head with a baseball bat means the word to her.
Of course, Nagi remains blissfully unaware of the fact Sachi has feelings for him, but hey, at least they’re talking again. Erika is clearly relieved that the vibes will improve
I remain unenthused at the prospect of a Sachi Route, and their accidental kiss could reasonably be held in contempt of the laws of physics, but it was true that Nagi wasn’t being fair to Sachi, and his adjustment in thinking was both welcome and arrived upon thanks to the friendships he’s forged with Erika and Hiro.