Warning! Spoilers ahead for My Hero Academia chapter 355!
Endeavor is somehow even more vulnerable now than he was during his then-lowest moment in My Hero Academia. This is really saying something since that the previous low moment in question is arguably one of the most emotional scenes in the entire series.
The torment that Endeavor put his entire family through is one of My Hero Academia's main storylines. It was clear from the beginning of the series that Shoto Todoroki shared a great deal of animosity for his father, completely rejecting using the portion of his quirk that came from his father as a result. Later, readers learned why and how Endeavor's actions affected everyone in the Todoroki family, including Shoto's older brother Toya who eventually became Dabi. Regardless, Endeavor always stayed reserved, even when he finally decided to make amends. So, when Endeavor finally broke down and cried in front of Shoto, both readers (and Shoto himself) were rightfully shocked, and probably still are. Never before had anyone seen Endeavor so vulnerable.
But now just a few panels in chapter 355 of My Hero Academia are miraculously topping that pivotal moment. By the start of the scene, Endeavor has already heard that Shoto has defeated Dabi. Endeavor's opponent All For One, capitalizing on how this news is clearly affecting Endeavor, begins mocking the number-one hero until he finds an opening and greatly wounds Endeavor. At the start of chapter 355, the number-one hero is lying in agony as a result of that wound, and it doesn't take long until his thoughts go to his sons as he calls out to them in his mind, desperately hoping they're okay.
This moment is massive for some many reasons but it's mostly because this is the first time that Endeavor is calling Dabi by his given name "Toya" and referring to him affectionately. Although Endeavor has known the truth about Dabi's identity since the Paranormal Liberation War, he's kept his actual feelings hidden until now. The act of calling out to him in desperation just confirms how he feels about Toya, which is exacerbated further by the direness of the situation. On top of this, fans have been waiting to see how much it has been affecting Endeavor to see Dabi and Shoto fighting each other. Even though it is Shoto's idea to battle, Endeavor still allows him to even though it is his own fault that Dabi ever became a villain. It is inherently off-putting to allow one's children to fight each other to the death. Seeing Endeavor suffer over his own morbid decision is heart-wrenching for readers and just adds to the overall unenviable position that Endeavor currently finds himself in.
What makes this moment a much lower point for Endeavor than when he initially bawled his eyes out to Shoto many chapters ago is the fact that Endeavor currently can't express his feelings to his sons even if he wanted to. The ability to apologize to or unburden oneself in front of the person one has wronged (especially a child) is incredibly cathartic. And it's now impossible for Endeavor to experience this, a fact that elicits a powerful reaction from fans. That said, the official translation of the manga does minimize this overall effect when compared with how the scene was translated by fans. In Shonen Jump, Endeavor only refers to Shoto and Toya as such and as "both." But in the fan translation, he calls them "my boys..." There is not a more personal or more emotional way for a parent to refer to their sons than that. But one thing is certain, this moment with Endeavor is quite a scene, regardless of which translation of My Hero Academia fans read.