Sharingan is a doujutsu ... the tragic death of someone dear. That's why Itachi unlocks it after seeing Shisui's suicide. Meanwhile, Sasuke awakens it shortly after killing his own brother ...

Itachi awakened his Mangekyo Sharingan due to Shisui's death, Sasuke did so for Itachi, and Obito awakened his for Rin. However, the motivations behind the awakening of this doujutsu differ from ...