The 'art style' tags are woefully underused.

I'd recommend eliminating the explicit watercolor tag and consolidating all such posts under a general 'analog' (hand-drawn art style) tag similar to pixiv:

http://dic.pixiv.net/a/アナログの本気
http://dic.pixiv.net/a/アナログ

There are a small number of posts on yande.re which would fall under that classification (such as colored pencil), but we only seem to have a watercolor tag.

Isnt this just a filter? dat $150 tho

Nah, it's definitely a scan. If you look closely at the paper you can see random dust/dirt, and the tool listed on pixiv is Brush w/ Transparent Watercolor (Talens Ecoline https://www.royaltalens.com/brands/talens/graphic-art-products/ecoline-liquid-water-colour/ ). He could be selling the original painting for that $150 rather than a print, but who knows.