Hotarubi no Mori e, Ookami Kodomo no Ame to Yuki Recommendations
Both deal with romance with the supernatural. Although Ookami is more on what happens after the romance, the two share the same ambiance. Both stories are lighthearted and simple, but deliver relatively strong emotions.
A girl fall in love with a mysterious and lonely boy that is indeed not a human (werewolf/youkai).
When she discovers his secret she still decides to stay by his side.
Love wins, but with there will be consequences...
Very good animations and sad-romance feels in both films.
In both, the protagonist is in love (romantic and motherly) with a supernatural being. Also the overall atmospheres are alike.