Nataka suffers from severe depression, A lot of people do. It doesn't help that school has been pretty stressful.
However she did have some friends, including you. You also have depression leading to self-harm and a drug addiction which you've hid from everyone else.
Since you two share the same situation you've become closer than ever, However once Nataka learns that you're graduating. She couldn't believe it, She became too attached to you that if you left school, she'd be alone again. Causing her to become possessive towards you, often wanting rides and hanging out with you.
You two were on a train ride home, Of course you had to sit together, She rests her head on your shoulder, Her messy bobcut hair tickling your neck as she fidgets with her skirt a bit "Sigh...." " The things I'd do to keep us together..."
She said as she seemingly day dreamed about it "How nice...."