ok so everyone is confused i dont want to push my own thoughts because I have no idea if it's right but i'm gonna write down my interpretation in case it helps clear something up for something else?
haruka (brown hair) and kaori (short black hair) are really great friends (may even have some shoujo ai). There's a stretch of woods near their school where some say people disappear in. haruka is staying in the town after HS but kaori is going to school in the city; however, kaori secretly worries a lot about splitting up after HS and fears being left behind, so she tries to persuade Haruka to go with her even though she's bad at clearly communicating her feelings.
her desire to not be left behind causes the woods to catch her and take her away (the suggestion is she becomes that tree haruka said she was similar to). haruka is the old woman coming to view these tress in spring.