User blog comment:Shaldemar/Prototype: Timeline (Light Novel Vol. 4 until Vol. 9)/@comment-29248623-20161018020040

I think the months are modeled after the Seasonal cycle of Spring, Summer, Autumn, Winter.

Summer should be fire and Winter should be water but I'm not quite sure of making this assumption. It would be easier to prove it if they matched a season event with a month or date stamp.