Oyasuminasai no Ato wa is an Alpha x Omega Manga. As you read the story you will learn the hardships of the Omega's and Alpha's lifes in their past and present.
It's cool how the mangaka took different steps and made the main characters in a relationship already, to focus more on their past and character developement (even tho I would have love to see how they met and how their feelings were built). Furthermore, I was a bit confused because in the beginning. It wasn't mentioned that the Sensei didn't know about Kotaru being an Omega. I felt like the story could have been more well built but I'm sure it was the mangaka's intention to draw and write it like that (since she wanted to complete it in a single volume + it gives the story a different touch to it).
To be honest, I'm no a fan of the art style but I still like that it differenciates from many other manga that I've read.
I really liked how the mangaka showed Sensei's and Kotarus past shortly after the beginning. Sakadachi KABANO really tried to put as much focus as possible on both characters. And she was succesfull. But I wish she would have also put a bit more focus in on Otsujiro. The child is such a cinamon roll, he really lightens the story up!
All in all, Oyasuminasai no Ato wa is a good read. It's not the best Omegaverse I've ever read but it isn't bad either, so give it a try!