Kurobuta Ouji wa Zense wo Omoidashite Kaishin suru: Akuyaku Chara ni Tensei shita node Shibou End kara Nigeteitara Saikyou ni Natteita

A black company's ex salaryman, Kurokawa Isao, reincarnated as a villainous prince of a game he used to play on repeat during his past life. What awaits the fat and arrogant "Black Pig Prince," Bratt, is a pitch-black fate in which he falls into darkness and gets killed. In order to avoid that tragic death ending, he endeavored in sword training, dieting and monster extermination. Even though he hadn't expected much out of it, Bratt began to gain the respect of the people around him...

(Source: Futabasha, translated)