S04E86 — The Most Terrifying Tutor

Tsuna's training with Hibari begins. During their battle, Tsuna is trapped enclosed by Hibari's hedgehog box weapon. Hibari reveals Tsuna will die from lack of oxygen if he does not escape. Tsuna, reaching his limit, prepares one final attempt to burn through the hedgehog. He burns a small portion and realizes that small portion is where the Vongola ring was. He realizes his X-Gloves flames must be equal to the Vongola ring's flames to break through. Tsuna collapses from the lack of oxygen. Just then, Tsuna's Vongola ring emits images to Tsuna's head and reveals the past crimes of the Vongola.