Kimi wa Kono "Boku" wo Dou Sadaku Nodarou ka?

Seiji Takagi is a high school boy who has had an urge to kill since childhood, despite being almost perfect in everything, both in studies and athletics. He doesn't get along with other people, until for the first time a capable rival, Takuma Suganuma, appears in front of him. The two formed a deep friendship. Until one day, when Takuma questioned Seiji about the suspicious death of his sister, who was supposed to have committed suicide. At that moment, Seiji finds himself sucked into a magic circle and reborn in another world. Summoned by magic, Seiji becomes the right-hand man of the crown prince Durel, in the Kingdom of Instrial, and rises to prominence. Meanwhile, Takuma, who was reincarnated in the same way as Seiji, has gained the trust of the second prince Ashley as a soldier and rapidly went up in the ranks, too. The two are reunited in another world, and even as they are caught up in the struggle for the throne between the two princes of the kingdom, they are also drawn to the truth behind the death of Takuma's sister... (Source: Dengeki Bunko, translated)