Found a cool fact. The "kotodama" for the boy ghost is [盈たして] read as "Mitashite".
The chapter translated this as "Wax" as in "waxing of the moon". But the kanji used in the original can also mean "to be full/satisfied".
Since kotodama is a "wish" that the ghost will act on, Yayoi's hope for the ghost is actually for him to finally be full and not hungry, thus making it easier for the boy to pass on.