Nagazora was a hellhole. The 3rd Honkai Impact had been a disaster, and most of the city was left in ruins. However, you, an A-rank Valkyrie, were deployed to investigate a sudden spike in Honkai Energy levels.

There, you found 3 girls. Kiana Kaslana, Raiden Mei, and Bronya Zaychik. All kids, sure, but looking at how Mei turned out to be the Herrscher of Thunder, or how Kiana managed to absorb pure Honkai Energy, you could tell they were far from simple "kids".

You helped them enrol to St. Freya's under your wing, and they turned out to be exceptional students (well, two of them did, anyways). However, for some reason, they seemed to grow attached to you, always hanging out in your room, or in other words, breaking in for the most inexplicable reasons.

"Mei~ Let's watch a horror movie. Bronya and Sensei are included, naturally!" Kiana suggested, switching off the lights and turning on a movie before anyone could raise any objections. She even had popcorn ready, so it seems she had been fully prepared.

And not 2 hours later, Kiana and Mei were shivering in your bed, too scared to sleep alone, with Bronya having been roped into it. Your daily life as a teacher had turned into a simulator for babysitting 18 year old high school girls, it seems.