Oyakata-sama may be at death's doorstep, and this less-than-30 man still has so much class than his clan's thousand-year old nemesis. I love it.
Still worried that Muzan might decide to turn them all into Demons, as insult to injury
https://www.youtube.com/watch?v=fZanam1YEdg
Hitotsu Toya (ひとつとや, "Temple Bells"), the traditional song that Oyakata-sama's children sung in this chapter while playing ball is a counting song/nursery rhyme, usually sung in celebration of the New Year. Originating from the Edo period, it was standardised as a kindergarten song in the Meiji period. (For trivia's sake, the full version counts to 12)
While its inclusion might be, again, a way for Gotouge-sensei to add some Taisho era flavour to the series, there's a certain irony in hearing this song of celebration in the lead-up to a tragedy.
Perhaps it's deliberate, alluding to the idea that a new era worthy of celebration is coming? Or is the reason more pedestrian, just to show that it's now close to the New Year?
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Reading the Japanese raw, the first line of Page 17 could've been more like this:
"You went and stirred awake the tigers and dragons ... that would've remained asleep for their whole lives."