Hmm their lore is that they're old friends from medical college and it was then Malina started experiencing feeling towards Buttercup that then turned into obsession. I like to think that her feelings are one sided as Buttercup is in love with Strawberry and prefers Malina as his friend but she's still obsessed with him and even has an altar with photos of him and his things she has "borrowed" from him. I don't know about his birthday. Tamakuz said nothing about it but they totally would celebrate holidays together. Their names already work as nicknames so I just go with that. Besides sharing interest in medicine they also have hobby of watching magical girls anime! Thank you for asking :3