Tomoe Tatsumi is a freshman attending university in Tokyo. Life couldn't be better: he's living in a really nice apartment for less than most people pay for a single room. This is all thanks to Mitsugu Kurokawa: salary man, landlord, and (hopeful) lover.
It is due to Kurokawa's generosity that Tatsumi is able to live in Tokyo on such a tight budget. Kurokawa's intention is clear: to love, honor, and cherish Tatsumi until his dying days! And if big brother Souichi Tatsumi has his way - that day will come sooner than not!
For Kurokawa, progress can only be made by "challenging the impossible...." And thus, Takanaga sensei introduces us to her charming romantic comedy, Challengers!
The main couple from Koisuru Boukun also have a few short chapters through out the manga that take place before Koisuru Boukun starts.