''I don't reach the 3 digits'' Theres no way someone her size wouldn't weight over a 100kg, unless they're in mars or they're growing gomu gomu style
I think she means "normally" less that 220 lbs./100kg, not when she's larger, with the implication being that she DOES add mass when she grows.
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It sounds like maybe she's a different Yokai, and the Hasshaku-sama thing is just other's perception of her due to the height thing? Maybe? I'm not familiar enough with JP folklore to have anything in particular come to mind.
Looking back at chapter 1, she originally sought Seiichiro's help after he comforted her + stated that Hasshaku-sama wasn't an indecent monster, when she was training to be scarier after she was fired from working at a haunted house as "Hasshaku-sama". So this most recent haunted house event isn't her first encounter with them, she used to work at one. It REALLY sounds like she did that because she was trying to strengthen her Yokai powers due to others' less-than-fearful perception of Hasshaku-sama, but maybe there's something slightly off there, either in translation or nuance.
Maybe she's a Yokai, cast as Hasshaku-sama at the 1st haunted house, and Hasshaku's image was negatively impacting Yachiru, who looked like Hasshaku-sama but was not her? Something like that? Hence how she can both claim to be Hasshaku-sama and not at the same time.