Ever since season 1, when these two met, it was amazing, their dynamic, Todo having flashbacks of nonexistent memories of them being at school living that slice of life set up, Yuji initially weirded out by Todo’s immediate attachment to him but eventually fighting side by side with amazing synergy, he might not really say it, but his actions with Todo, the complete trust has always been in display ever since, whenever they are fighting together. This bond was in full display when after bringing Yuji back with his amazing speech, Todo proceeded to fight Mahito, just when Mahito thinks he’s got Todo, Boogie woogie activates and Yuji is not standing infront of Mahito, already charged for a punch. He gathered himself and prepared to be tagged in. Todo knows and wants for Yuji to get his get back, Yuji knows Todo will tag him in, so he preemptively assumed the stance and charged, Todo being the Goat that he is, the perfect moment to catch Mahito offguard, Yuji appears and unleashes one of the weightiest Black Flash of the season, one that apologizes for his cowardice, paying respects and sending Nanami off properly.
Action is empty without context, and with all that Yuji endured up to that point, that Black flash was rich and full of it.