When Tsuna and the others returned to the past to train before their upcoming battle with the Millefiore along with Uni, Uni summons Vongola Primo from the Vongola Ring and was told that the First Guardians of Vongola will observe them henceforth to see if they are worthy enough to inherit the Vongola's true power or not. At night, he appears from the Rain Vongola Ring in front of Yamamoto in the middle of his training. After introducing himself, he requested to hear the extent of Yamamoto's resolve. When Yamamoto gave a simple and clear response, he laughed and said that he will observe him carefully.
Rain Guardian Succession Trial Edit
Later, when he prepares to give Yamamoto his test, Yamamoto assumes that he is supposed to fight him and defeats him while accidently injuring Colonnello. This results in Yamamoto's defeat, which is questioned by Tsuna. Ugetsu said that Tsuna already knows the answer. Ugetsu decides to give Yamamoto a second chance but warned him that there won't be a third. Yamamoto, however, passes the second round when he realized the true meaning of being the Guardian of the Rain. Yamamoto and Ugetsu got along very well after that; both stating they enjoyed battling each other. He gives his power to Yamamoto and states it will be useful when he's in a dire situation. He was later seen with G., who commented that he was too soft. He said to G that Decimo's Family reminded him of the past with Primo's Family.
Later, at Namimori Shrine, he, along with the other Guardians and Primo, meets to discuss the trials so far, and the one that was yet to come. All of them look worried since the next trial would be Demon Spade's succession test.
The Guardians watch the trial from afar and consider interfering. However, Giotto stops them and asks them just to wait and watch.After Demon Spade's trial finished, he along with the other guardians and Giotto returned to the Vongola Rings.
He appeared from Yamamoto's Vongola Ring during Tsuna's battle with Byakuran, along with Giotto and other guardians. He told Yamamoto and the others that they were always by their side and stated that Tsuna was indeed carrying their will, which allows Giotto to bestow Tsuna with the true form of Vongola Rings.