Obsession is a very common theme. The yandere character is often overly obsessed with the object of their affection. For example, in 'Killing Stalking', the yandere character's obsession drives a lot of the dark and disturbing plot.
One common characteristic is extreme possessiveness. The yandere father will often see the other male character as his sole possession and get very jealous if anyone else gets close. Another is overprotectiveness. He may go to great lengths to keep the other safe, sometimes in an overbearing way.
One popular yandere father BL web novel could be 'I'm in Love with My Father'. In this type of story, there are often complex relationships and intense emotions. The yandere father character might show possessive and overprotective behavior towards the other male character, creating a unique dynamic full of drama and passion.
Another great one could be '19 Days'. It has some yandere - like behaviors in the relationships between the characters. It also has a great art style and engaging plot that keeps you hooked as you explore the BL relationships within.
Yandere male characters in manga usually show an intense, single-minded focus on the object of their affection. They might seem charming at first, but their behavior can become unstable and dangerous as their obsession grows. This can make for a thrilling and dark storyline.
Yandere sister manga often feature intense and obsessive emotions. The sister character might be overly possessive and show extreme behavior towards the protagonist.