Warau Nemesis: Anata Dake no Fukushuu

Shunsuke Suzuki, who works at an advertising agency, spends his days being abused by his strict trainer Kojima. While thinking about quitting the company and wishing Kojima had died, Suzuki happens to see a commercial that Kojima made. The commercial shows a project that Suzuki had thought up and Kojima had rejected. Kojima had taken Suzuki's other projects as his own. When Suzuki confronts him about it, Kojima doesn't apologize, he just gets angry. Seeing Kojima come to work as if nothing had happened, Suzuki finally feels murderous. Then, as Suzuki searches the internet for ways to commit the perfect crime, a mysterious person named Yamino appears, telling him that he should get revenge in his own way...

(Source: Natalie, translated)