This topic has a lot of terms to cover, so I've decided to split it into 3–4 parts to make everything easier to understand.

Definition: A main character who lacks typical heroic qualities, such as kindness, honesty, or selflessness. Example: Classroom of the Elite — Kiyotaka Ayanokoji, who often uses manipulation to achieve his goals.

Definition: A villain who has understandable goals, good intentions, or admirable qualities but uses harmful methods. Example: Naruto Shippuden — Pain (Nagato), who wants peace but uses violence to pursue it.

Definition: A character whose contrasting personality highlights another character's traits. Example: Death Note — L and Light Yagami. Their contrasting personalities and methods highlight their intelligence and beliefs.

Definition: A story that examines a genre's familiar ideas realistically, exposing their darker sides or hidden problems formula. Example: Puella Magi Madoka Magica — challenges the usual cheerful magical-girl formula.

Definition: When a character returns to worse behavior, old flaws, or an earlier stage of emotional growth. Example: Vinland Saga — Thorfinn initially becomes consumed by revenge, which holds back his emotional growth.

Definition: The journey through which a character changes, learns something, or becomes a different person. Example: Vinland Saga — Thorfinn changes from a revenge-driven fighter into someone who seeks peace.

Definition: A struggle inside a character's mind, involving fear, guilt, desire, or conflicting beliefs. Example: Neon Genesis Evangelion — Shinji Ikari struggles with his need for acceptance and his fear of rejection.

Definition: When a character's actions cannot be clearly classified as entirely right or entirely wrong Example: Fate/Zero — Kiritsugu Emiya makes cruel sacrifices in pursuit of peace.