Yandere Pre-War Master is a mix of classic villain and Gomez Addams.
The Doctor is far more unhinged. Mfer was capping people and sword duels the master.
Imagine the two idiots fighting in the middle of their plots, the Daleks and the British awkwardly standing on the side like "Are we interrupting?"
The current companion offering consolation to the Timelord Darling who might just regenerate from embarrassment. A dalek offers a handkerchief in mock kindness.
Timelord Darling is standing at the side trying to fix the latest fuck-up of the two. All the while they're playing swords! For all of the galaxy's sake, why were you stuck with these two intelligent, obsessive morons.
( Yandere ) The Master is constantly trying to romance darling. He goes too far with it. To an extent it's terrifying, but there is also this allure. It's an inexpcible pull. Well, you could explain it. It just would take far too long. They'll have a rose in their teeth and someone's head on a pike, and you can't help but be attracted.
But he's The Master. You can't fall in love with them. You are disgusted (?) by him. Revolted (?) You can't quite pinpoint. Or maybe you're just scared to be in love with him. To be as obsessed as they are.
( Yandere ) The Doctor is just a whirlwind. One moment it's this and another it's that. You are always on the cusp of another adventure with him (even if you don't want to). Everyone fears him with the exception of The Master. Even the Daleks hesitate to get near you because of The Doctor's wrath. Sometimes he's a ball of fun and other times he's sly (manipulative―borderline evil).
But he's The Doctor. He helps people. He can't be all that bad, right?
Together, they are an unstoppable yandere duo.