Haruka is something like the ruler of highschool and everyone obey him without arguing back, except Mario. A freshman that defends his class with everything he has. This has only serve to catch Haruka's attention and now he's over Mario all the time, determined to make him fall for him.
On the other hand, we have Yujiro, Mario's friend, and Masaomi, childhood friends that grew up together as family. Now, after some incident, Masaomi confessed and Yujiro agree without being fully aware of what was going on and since then, Masaomi has started to be moody and going into sex-beast mode with Yujiro every single day.
Lastly, there are Shizuka, Masaomi's older brother and Miki, a freshman Mario and Yujiro's friend. Miki is so in love with Shizuka but Shikuka is afraid of be let alone after give in to his feelings, that's why he is so cold towards Miki after sex and why they're not officially dating. Thank god, Miki won't give up.
Umegatani Danshi Koutou Gakkou - Kuro Oujitachi no Koi