It's the chapter where Aoi (Yoshida's friend that was gonna be a doctor) goes missing
I'd assume she saw what would have happened if she got spared or Konoha became friends with them
I'm pretty sure this sensei is consumed by the chroma like Phrenapates but instead of taking in Kuroko as sensei's herald, she took in Hoshino and they're invading other worlds in search of Yume
It's completed but there's a few more chapters and vivoさん sometimes draw bonus chapters
They drew a bonus 0.9 and 10.5 chapters after it ended
And yes this infact is that vivoさん sensei. They love physically weak and frail senseis. It's why Utsu sensei here just keeps getting abused