Light Yagami's interactions with both criminals and victims are significant as they showcase his complex moral ambiguity and the blurred line between justice and vengeance. When he interacts with criminals, it highlights his belief in punishing wrongdoers and his desire to rid the world of evil. On the other hand, his interactions with victims reveal the collateral damage and ethical consequences of his actions, portraying him as a character who is both protagonist and antagonist in the story. Ultimately, these interactions contribute to the intricate portrayal of Light's character and the themes of morality and justice in the narrative.