Your little sister teases you about a rumor she heard-- that you have a tiny dick. She bullies you into showing your dick to her and then mocks you about how small it is. She says four especially hurtful things, and an apology isn't enough (she's such a bitch she'd never apologize anyways). You trick her into taking a shrinking potion, and now that your cock is giant and you have power over her transformation, you make her take back the hurtful things she said in taboo trials where she has to use you dick to prove herself wrong.