Look for fanfic communities dedicated to the source material that Phobos and Will are from. There, you can ask for recommendations of 'yandere phobos x will fanfic'. Members are usually quite helpful in sharing their favorite stories in this genre.
Once upon a time, there was a yandere anime girl named Ayumi. She had done something terrible to the boy she loved. One day, she finally mustered up the courage to apologize. She stood in front of him, her head bowed low. 'I'm so sorry,' she said softly. The boy was initially shocked but then saw the sincerity in her eyes. Ayumi continued to explain how her intense love had made her act wrongly. In the end, the boy forgave her, hoping she could control her yandere tendencies.
She might have made false accusations against the people around her love interest due to her insecurities. When she found out the truth, she felt ashamed of herself. So she apologized to make up for the trouble she had caused. Also, if she had tried to isolate her love interest from his friends and family, she could apologize when she understood how wrong it was.
Well, 'That Time I Got Reincarnated as a Slime' can be considered in this regard. Rimuru, the main character, experiences an isekai adventure, and there are some characters with possessive or extreme loyalty traits that could be loosely related to yandere. Also, 'Log Horizon' is an isekai novel where the characters' relationships and their growth in the new world might have some yandere - like undertones at times.
There's also 'The Yandere Male Kagome's Quest'. This one is different as it focuses more on the male Kagome's journey while still maintaining his yandere traits. He goes on adventures, all the while being possessive and overprotective of the people he cares about. It's a unique take on the yandere concept in a fanfiction setting.
One popular 'yandere x kagome fanfic' is 'Obsessed Love'. It has an interesting plot where the yandere character shows extreme possessiveness towards Kagome in a rather unique Inuyasha - inspired setting.
One interesting 'oc x yandere chan fanfiction' could be the one where the OC is a new student in the school and Yandere - chan becomes obsessed with protecting them from other students she deems as threats. It's a unique take on the relationship as it shows a different side of Yandere - chan's possessiveness.
In yandere x reader fanfics, yanderes usually display intense emotions. Their love for the reader is not the normal kind; it's more of an obsessive love. They may have a dual personality where they can be extremely sweet and loving one moment, but if they feel threatened in their relationship with the reader, they can turn very dangerous and menacing.