Here they are, Volume 1's extras. I put them in between the chapters rather than compiling them at the end cause I felt like this would be nicer when starting from chapter 1 to have all the extra chapters right after the chapters they belong to (just like in the actual volume).
The first extra manga is pretty interesting as it provides some backstory to when Sainami and Kuno first met.
The title mentioning April implies that it's set near the start of the school year, and Sainami's appearance resembles the flashback appearance from chapter 1:
As well as Sainami wearing a tracksuit, which is another nod to the first chapter where Sainami tells Kuno that wearing a tracksuit isn't going to solve anything. This is also probably close to when Sainami turned into a girl.
Also interesting tidbit is that the 3rd extra was already uploaded to Pixiv back in January. There are two more extras on Pixiv that I probably won't be translating for now, since they will probably end up in the volumes later on.