WARNING: The following contains spoilers for Boruto: Naruto Next Generations Episode 175, "Beyond The Limits!" now streaming on Crunchyroll.
One of Boruto's biggest mysteries has been how Sarada unlocked her second tomoe in her Sharingan eye. These tomoes keep evolving the Uchiha clan members, allowing them more abilities. The manga had her unlocking her third one when she fought Kara's warlord, Boro, but no one knew how she went from the one she started the series with to two. This finally comes to light in the anime because of something that mimics an iconic Naruto and Sasuke moment from the original Naruto.
With Deepa preparing to eat her and Boruto in the Land of Valleys, Sarada knows she needs to be better than their first encounter. She has to help bring the God Tree clone down, but first and foremost, Team 7 needs a new strategy against the psychopath. He's still outlasting them despite her training with Sakura and Naruto upgrading his Rasengan, but things look a bit better when Mitsuki joins the fray.
Sadly, Deepa continues to level up, proving that his experience and drive to devour the tree's chakra fruit is way too much for the kids to handle. It leads to a brutal exchange with Sarada trying to dodge his missiles and Boruto also shooting off a Rasengan. Despite all that, and even Mitsuki unleashing all his snake abilities, they're pummelled by the madman, which leaves a window of opportunity to murder Boruto.
As Naruto's son lays on the ground badly wounded and struggling for breath, Deepa unleashes his missiles at lightning-fast speeds which are more or less unavoidable. However, as Sarada cries out for Boruto, she moves so fast, it's as if she harnesses Sasuke's teleportation abilities. It turns out her speed and strength increased, and as she blocks and destroys the iron pellets, she looks up to reveal her second tomoe unlocked. Her emotions spilled over as she thought she'd lose Boruto, and this allows the change as is usual for the clan.
This big scene plays like a throwback to Naruto and Sasuke fighting Haku. There, the ice-ninja would create spikes and use them as blades, and just as he was about to finish Naruto off, Sasuke sped over out of nowhere to take the brunt of the hits in Haku's ice castle. This proved to Naruto that Sasuke had some good within him, and as this was their first mission, he'd be inspired to spend his life trying to surpass Sasuke.
Interestingly, the first hints of Naruto's Nine Tails chakra from Kurama appeared when he saw how Sasuke was damaged, which teased that Naruto was indeed a WMD. Here, Boruto realizes Sarada sacrificed some of her body to save him but rather than turn feral, he begins recalibrating his Rasengan for further damage so he can now protect his teammates.