Supportive parents in manga? What sorcery is this?!?
Also, proceed with baby making, Yuki can't be a virgin forever.
There's some, odd, clues:
1. Mom calling Yukio a Yukiko.
2. Hikikomori as an old habit of Yuki.
3. Yuki used to make female pronouns, but male around Kou.
4. Yuki didn't go to high school, for some reason.
5. There's something unsettling with Yuki photo holding scissors and it isn't most likely about cutting hair.
6. The potted plant clearly says 3rd year of high school, despite Yuki saying that she didn't, which is a way to tell a person died or if alive should die. Tho' a white flower or chrysanthemums are used unless someone was extra petty...
I'm hoping to just be paranoid, don't ruin my wholesome story...