Ryohei Sasagawa vs. Koyo Aoba is the second major battle of the Inheritance Ceremony Arc; it features the tenth generation Sun Vongola Famiglia Guardian and the tenth generation Forest Simon Famiglia Guardian fighting over their mutual pride, boxing.
As Reborn, Tsuna, and the remaining Guardians travel to their "goal", they arrive at a huge forest. They eventually encounter Koyo Aoba, who attacks with an intimidating wave of Flames but left the group unscathed. When questioned by Ryohei, Koyo admitted that his hate for the Vongola surpassed his love of boxing, but that he would use it to defeat them. Ryohei, however, demands a one-on-one boxing match, stating this was his pride. Koyo agreed, unleashing a barbed Forest Flame around them to act as the ring. Koyo announces that whoever was forced to his knees first loses, but that Flames and foul play were also allowed. Koyo then released an overpowering Flame. Unfazed, Ryohei then activates his Vongola Gear and goes into Cambio Forma. Surprisingly Koyo claimed to already know of Ryohei's abilities and the three minute time limit. He went on to reveal that the Simon had a spy in the Vongola, someone who was greatly disappointed in the Famiglia. Remaining composed, Ryohei stated that as well as having a new indefinite time limit, his Vongola Gear had other new features. The two then square off.
Early on in the fight, Koyo seemed to have the upper hand, using his flame to surround Ryohei both restraining and blinding him allowing Koyo to beat him senseless from all angles. As Koyo prepares to deliver another fist, Ryohei unleashes a devastating attack out of nowhere causing a huge explosion that Koyo narrowly avoided. Koyo, seemingly surprised that he still had such strength in him deduced that this was the Vongola Gears new feature. Ryohei then revealed that his new power was to convert the damage to his body into new attacks and that that attack was only at a third of the bangles capacity. Koyo laughed at this pointing out the damage he had already taken. However Ryohei responded by claiming that as he had revealed his power he could fight without holding back. Ryohei then charged at Koyo, avoiding his flame attacks and closing the distance. Koyo responded by unleashing a barrage of punches that Ryohei was only just capable of avoiding. However Reborn pointed out that he was charging his flames by purposefully letting Koyo's attacks graze him. Ryohei then unleashed another blow that sent Koyo flying and knocking off his glasses. However, Koyo revealed that he could now fight at his true strength. Finding his glasses Lambo expressed surprise that he couldn't see through them.
Koyo then extinguished his flame claiming that he wouldn't need it. Ryohei once again tried to graze the attacks; however a single attack caused him great pain. Koyo then explained that his glasses were designed to limit his incredibly powerful eyesight – and without them he could pinpoint Ryohei's Killer Points – points in the body that change constantly, but are deadly to the person if struck there even with light attacks. Koyo then attacked again causing Ryohei's Bangle to reach sixty percent. However Ryohei noticed Koyo's rushed behavior and jeered at him. This sent Koyo over the edge causing him to attack with flames as well; however, before he could do so, he momentarily lost his eyesight and giving Ryohei a chance to make a direct hit. Reborn explained that the overuse of his eyes had caused them to overheat due to Koyo being unable to continuously process the massive amount of information.
However, despite suffering huge damage, Koyo survived the attack and was still able to fight. Reborn pointed out the recklessness of his decision, proving Koyo's determination. Ryohei apologized to Koyo, stating that he must defeat him at full power. The battle then became a race with Koyo trying to take Ryohei down before his eyes gave out and Ryohei trying to stay conscious long enough to charge his flame. Koyo comes out with the upper hand, fatally striking all Ryohei's killer points. With several bones broken in Ryohei's body, Koyo strikes him in the face. However Ryohei used this opportunity to grab Koyo and with his flames at 100% he delivered a catastrophic attack that cleared the whole area of forest in the resulting explosion. As the smoke cleared away, it was revealed that not only Ryohei but also Koyo was still on his feet. Astounded Tsuna and Gokudera tried to comprehend what drove them, to which Reborn responded that their pride was beyond what he could have imagined. With both combatants unyielding and unrelenting, they charged at each other, crossing fists once more before succumbing to their injuries and collapsing.
Due to the fact they both collapsed at the same time, the Vindice appeared, took both of them away and left them the first of seven visual "Keys."