Based on the first few pages it sounds like a sequel, but checking his older works on this site I couldn't find anything, so maybe the prequel is from a much older magazine issue?
That first page certainly leaves an impression, I'd say.
"What choice do I have, I'm being threatened ❤"? Yeah...Not very convincing when you stick a heart mark at the end, eh?
Great ending though. I guess he basically came up with that threat/blackmail out of jealousy even though he doesn't actually have it on hand. And it turns out he was just misunderstanding their relationship so hey, I'd say it worked out fine. Shouldn't be any problems if they go out after he graduates.
Part of me can't blame young Katakura-kun for reacting as he did when he saw Chika-sensei being approached by another teacher; granted he apparently didn't stick around to hear their entire conversation. Of course, it's debatable whether he's truly attracted to Chika (sign of his potentially becoming A Man Of Culture) or if it was simply the thrill of losing his virginity.
It was also rather cute how, when everything was revealed, he admitted that he tried the blackmail route out of jealousy, which definitely fired up Chika with a sense of being in charge of any budding relationship.
Granted, another time, place and artist, this whole scenario could have become something downright ugly, so I'll just leave things as they are by saying:
"The story you are either about to read or have just read is true ... the names have been changed to protect the innocent."