because sometimes, being just plain awesome... isn't good enough.

During the Varia Arc. The boys Reborn chose to be Tsuna's guardians each recieve half a ring to show their status for when they battle against the 7 Varia members. Each Varia member represents one of the seven deadly sins: Lust, Envy, Sloth, Pride, Avarice, Gluttony, and Wrath, as such it is only appropriate that the other seven (Tsuna and his friends) be just the opposite. They have the Seven Virtues: Chastity, Charity, Zeal, Humility, Generosity, Moderation, and Patience. Ryohei fights Lussuria who stands for Lust and therefore that makes him Chastity, which in better terms would also translate as purity.

Ryohei is pure in many ways. Ryohei was not originally involved in the mafia and he doesn't seem to see the cruelty in the world. It is more likely though, that he chooses to feign ignorance in order to find enjoyment in a cruel world. He fights to protect his family and friends and he doesn't fight to hurt or kill an opponent. He finds that every unfair fight is just a chance for him to improve rather than a form corruption or cruelty. Ryohei also forgets important details a lot, and purity, being similar in definition to innocence could fit Ryohei quite well. Ryohei's bad habit of remembering things and love for life and all thing EXTREME! makes him seem completely innocent and blind to the world. If you can't remember something terrible you'll be unaffected by it. At least I believe so.