The cutest things could include always having a kind word when you're down, or doing a little dance to make you laugh. Sometimes, it's the way they remember the tiniest details about you that's just adorable.
There are many possible reasons. Maybe the childhood friend had always secretly loved the protagonist and couldn't handle any competition. Or, some trauma or insecurity could drive them to be obsessive. Another possibility is that misunderstandings or external pressures played a role.
Often, these mangas have a storyline that plays on the nostalgia and close bond of childhood friendships. They might include fantasy elements or unusual situations to add to the excitement. The characters' expressions and poses are designed to be highly provocative.
Often, a cliche childhood friend onee-san manga has repetitive tropes like the childhood promise that always comes true or the overused protective older sister stereotype. Also, the story might lack depth in character motivations and have very straightforward story arcs.
First, try to reconnect with your childhood friend and remind them of the good times you had. Then, gradually build a deeper connection by sharing your current interests and dreams. Maybe plan some special outings or activities together to strengthen the bond.
It depends. If the portrayal of the yandere girlfriend is done in an interesting and nuanced way, it could be appealing. But if it's overly stereotypical or one-dimensional, then no.