WARNING: The following contains spoilers for My Hero Academia Chapter 349, "Battle Flame,” by Kohei Horikoshi, Caleb Cook and John Hunt, available now in English from Viz Media.
Uraraka Ochaco and Tsuyu Asui's diversion in My Hero Academia Chapter 348 gave Midoriya Izuku the momentary respite he needed to flee Okuto Island and head for UA. As Deku rushed to face Shigaraki as fast as he could, he received a vision of the second wielder of One For All, who warns him about the danger of overexerting himself before arriving at the fight -- but that worry seems almost trivial compared to the situation Uraraka and Tsuyu might have to face soon.
Midoriya headed for UA using a combination of three of One For All's abilities: Float, Fa Jin and Air Force for propulsion. Blackwhip might have increased his speed as well but as he was traveling across the open sea, there was nothing he could attach its tendrils to in order to sling himself forward. In his hurry, Midoriya didn't realize he was making questionable decisions and using his power more wildly. Luckily, the second One For All user appeared to him in Chapter 349 to help clear his head.
The second user, whose name still hasn't been revealed, admonished Midoriya for risking the damage of his equipment before he even fought Shigaraki. Once Deku had calmed down, the mystery person asked him if he had tried using his own Quirk -- the last one locked within One For All. When Deku replied in the affirmative, the second user reminded him that this Quirk was only to be used as a last resort.
After years of mixing with One For All, the second user's Quirk had become far more powerful than it was during his own lifetime, and carried the risk of going as wild as Blackwhip did when Deku first unlocked it. The specifics of the Quirk haven’t been revealed yet, but it might be just the tool needed to counter Shigaraki's new body augmentation ability.
Meanwhile, the fight between Uraraka, Tsuyu and Himiko Toga continued to rage. Following Midoriya's departure, Toga made a startling declaration: even though she still loved both Uraraka and Midoriya, she couldn't be bothered about either of them anymore. She promised to carve her own path as Toga and continue to live life on her own terms, then contended she has no need for heroes and implied that she'd defeat Uraraka soon enough. Undeterred by her opponent's rants, Uraraka threw Toga's words back at her and stated that she would follow her own desires as Uraraka Ochaco -- but she may have bitten off more than she can chew.
Before MHA's biggest war began, Toga came into possession of the last of Twice's blood. It was gifted to her by Dabi who knew that she'd be able to access his Quirk, Double, once she ingested it. Double is a very simple Quirk but also extremely powerful. It allowed Twice to singlehandedly overwhelm the entirety of the Meta-Liberation Army and was so dangerous that the #2 Pro Hero, Hawks, decided to take Twice's life rather than allow him use it as he pleases. Now, it looks like that deadly power is finally coming back into play.
Toga probably didn't use Twice's blood right away because she wanted to hear Deku's answer to her questions. Now that she's free of all attachments to the UA students, it seems like she's finally about to take the battle seriously as My Hero Academia continues. Triggering a "Sad Girl's Parade" in the midst of the accompanying Nomu's rampage would disorient the heroes even further -- and may shift the battle strongly in the villains' favor. However, it also provides an opportunity for Uraraka and Tsuyu to rise to the occasion, showing off the fruits of their last few months of training.
