Reborn - Episode 51 "Illusion VS Illusion"

Tusna have found out that Chrome Dokuro is the Vongola's representative of Guardian of the Mist, Tsuna acknowledges her as a part of the family and allows her to take part in the duel.

After many exerted attempts to attack 'Mammon' (now known as Viper of the indigo pacifier), Chrome eventually loses to the illusions.

However, the battle does not end and an unexpected person comes in to assist in the battle.