It's a pretty rough situation on all sides, frankly, I don't understand the people acting like Sena's the villain here.
She seems like a very emotionally reserved person, but her coldness doesn't seem like a reflection of her actual feelings, given that frustrated outburst. Yes, she is objectively neglecting Shigusa and failing to communicate with her why, but I can definitely understand where she's coming from with trying to balance her responsibilities, and I never got the impression she didn't actually care about her girlfriend, despite the poor choice in deprioritizing her. She probably should have broken up with her in order to not just leave Shigusa handing all the time, but at least she cancelled the date, instead of standing her up altogether. And I can only imagine how much additional stress Sera's stunt at the end will add on to Sena, probably pushing her sister into severe burnout even in the 'best' case scenario, and potentially have even worse consequences.
Sera... I'm sympathetic to her, but only to a point, and the date under false pretenses was one thing but the level it escalated to is objectively rape by deception. That's no bueno.
I'm kinda disappointed this is part of a oneshot anthology, because a followup exploring the consequences of this could be fascinating. As-is, it's still compelling, even if I'm left kinda wondering what the overall point was.