Sotsugyousei (Sequel)
Sora to Hara (Spin off)
O.B. [Occupation to Beloved] (Spin off) - sequel to Sora to Hara
Doukyuusei & Sotsugyousei Fanbook (Side Story)
too lazy to look for it myself but did you check these?
http://www.mangago.zone/read-manga/graduation_certificate_artbook/
It's in the first chapter...the only chapter...
http://www.mangago.zone/read-manga/doukyuusei_nakamura_asumiko/tr/v01/c009/pg-1/
This is where they buy the rings.
I really wanted them to have a proper proposal. Not just the one in the artbook. I hope sensei will continue their story. I think O.B. is still ongoing, so there is hope.
I really love the series and the anime was amazing :)
I am desperately searching for this chapter where Kusakabe or Sajou turned 20 and they proposed to each other.
I remember reading this chapter and now I going mad because I cannot find it!!!!!
A link to it would be VERY MUCH APPRECIATED T^T
Thank you