I do like that this 5 chapter arc basically served as a relatively big step Senpai, in terms of development, not only realizing his feelings of wanting to be closer to Nagatoro but also to subtly tell her that he wants to be closer to her by wanting to know her first name.
Some may feel like his backing out of asking Nagatoro's name is something of a beta move, however you must think of it like this. In the past 5 chapters, and even a little bit before that, Senpai is starting to realize that Nagatoro might like him. In his turn, thanks to some prodding from Nagatoro's sister, he's finally able to admit that he's interested in Nagatoro. However he doesn't want to rush things. Senpai wants to make sure things go right and no development in thier relationship is made based on some forced obligation, like a bet.
Also considering that the last encounter they had in chapter 58 didn't put Senpai in the best light in Nagatoro's eyes, Senpai probably thought that forcing Nagatoro to reveal her first name to him, which is a serious thing is Japanesse culture, might serve only to make things worse in the long game.
The fact that Senpai told Nagatoro that he wants to know her first name, implying that he wants to be closer to her, show that Senpai has come a long way from those first 10 (or even 30) chapters. Plus the fact that Nagatoro is more than aware of what Senpai meant and is not only accepting of that but also moved by that gesture (like I said in a previous comment, Nagatoro calling Senpai gross is like Westley from the Princess Bride saying "As you wish.") says a lot as well.
Like many of you, I also want these two to just start dating so that we can see how their dynamic is affected by the added element of a romantic relationship. But as long as we can get more insight in how Nagatoro and Senpai mean to each other and how their current relationship affects their character, I'll personally be fine for now.
And also the sister was so going to reveal Nagatoro's first name, even if she won the bet against Senpai.
