This story is of the begining of the three new captains and there three new friends.(original characters)
The three new captains are 3rd squad- Hyko Uskame,5th squad- Yokae Shujiro 9th squad- Kensai Kinosa.
They each bring new people who become there co-vice captains along w the already existing vice-captains.3rd squad- Kira Izuru and Nadarutiko(Nada) Nara, 5th squad- Momo Hinamori and Ami Shujiro(Yokae and her are like sisters), and 9th squad- Shuhei Hisagi and Mizuru Mizuki.
The events starts right after Aizen betrays soul society. There are time skips in the story btw.