

The character is casually immune to an almighty power
Tom Bombadil (Lord of the Rings): The one ring’s powers have no effect on him, he can wear it without corrupting effect, can see Frodo when he turns invisible, and can do magic on it. However, he is not selected to join the fellowship because he doesn’t recognize the importance of the one ring powers and therefore a potential risk is him misplacing it.
Luffy (One Piece): He has two immunities. The first one was the Goro Goro no mi, which due to his rubber body, makes him completely immune to electric attacks and then later on, and this isn’t even related to his powers or anything, he’s unfazed by Boa using the Mero Mero No mi on him (that fruit turns the user’s own emotions towards Boa, specifically attraction due to her beauty, against them and turns them to stone).