[ The smile attempt somewhat gets Zenitsu to relax just a little. His ears not being as keen as it should, he's still a little wary, however.

Overly serious is a perfect description. It even gets worse when Tanjiro's involved, too. It reminds him of when the three of them went on a run around the city as training even though Zenitsu wanted a break. ]

I can see that. He treated the new year mini-game as a training session.

[ mAYBE he shouldn't keep talking about someone who's no longer here. Thinking of someone who he can no longer speak to reminds him of his own teacher, and that depresses him. Instead, he decides to shift is attention over to the other doll. ]

Who's the other person? Are they your family, too?