When Tsuna and his Guardians come back to the past to train before battling with Millefiore Famiglia along with Uni, they summon Vongola Primo from the Vongola Ring, and were told that the First Guardians of Vongola will observe them henceforth to see if they are worthy to inherit the true power of Vongola or not. At night, he appears from the Lightning Vongola Ring in front of Lambo while Lambo was on the toilet at the same time as the other Guardians.
He commented on why the Decimo Lightning Guardian is a "little cow boy", much to Lambo's anger, then disappeared in irritation.
At first, Lampow refused to even waste his time testing Lambo, stating that he was a snotty brat, but Giotto found him and made sure that he did his duty, to which Lampow replied that he "can't say no to you, Primo." During Lambo's test, he hid inside a castle inside the amusement park, and the only objective was for Lambo to acquire three stamps and go to him. This shows his obvious distaste for Lambo and the fact that he had not been prepared beforehand, as stated by Reborn; however, Verde's interference made this a more difficult task as he had shocked Lambo with an electrical charge and sent robots after them. When Lambo, along with Tsuna, eventually reaches the castle, Lampow rejects Lambo at first because the required stamp was on Lambo's butt and not on the paper, but then agrees to accept Lambo on the grounds that Lambo had fulfilled his role as the Guardian of Lightning by acting as a lightning rod for the entire family and taking the damage onto himself and after witnessing Lambo's furious lightning bolts. After the explosion in the castle caused by Lambo reviving and randomly tossing his grenades, Lampow reappears on the roof of the castle and declares that he "still hates brats."
Later, at Namimori Shrine, he along with other the Guardians and Primo meet 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. At Kokuyo Land, he, along with Giotto and the other guardians, were watching Demon Spade's trial from afar.
After Demon Spade's trial ended, he, along with the other Guardians and Giotto, returned to the Vongola Rings.
While Tsuna fought Byakuran, he appeared, along with Giotto and the other Guardians from the Vongola Rings after witnessing Tsuna's resolve.