Again this breast fetish. I wonder if Mangaka simply ignore the ideal of elegant breasts [there are many Graeco-Roman statues providing some aesthetic insight about a good female figurine] or if Japan simply has become a land where pop culture needs to tend to the preference of female bodies that look as if they already gave birth 1-2 times...
Especially for a wind spirit, I would've imagined a more aerodynamic form.
If we go by symbolism, it's usually the earth-/harvest/fertility goddesses&spirits that have a maternal look.
And if they go for maternal look anyway, they could as well just make a widow/divorcee in her mid 30s or early 40s the main female love interest of the main character. But maybe that's a bit too deep into the Seinen genre rather than Shounen[this is supposedly Seinen; looks like Shounen to me,though].