This manga is centered on sticks and carrots.
Whoever has the highest incentive wins Sensei.
The characters look a little old-fashioned, but the art style very successfully conveys strong emotions the mangaka felt through the characters at most points.
However, the plot lacks a perspective on how Sensei ticks. He is rather silent during critical conversations with minor characters, thus readers might not understand why he made his choices. Unless you try to empathize with each role played by a character in varying situations, (Takagi a caregiver towards Sensei, mean toward his subordinates) it helps to see the motive for an action.
Personable characters. Takagi is a high performer in work and relationships. It takes an emotionally advanced one like him to capture people such as Sensei. There are not many people of this pure love kind in the world, though. Since this is Mafia, Takagi typically forces Sensei at first into the abyss. Then he tries to corner Sensei by tangible means. As the plot progresses, Takagi realizes there's no other way than offering something intangible, excluding his heart, that makes him special compared to other potentially suitable candidates in sensei's eyes.
Sensei seems to be psychopathic, due to his objective judgement of even those close to him. He does not seem to have a conscience, which attracts trouble to him. Not being able to live without drama, he wants an SO who can keep up with a Korean drama-like relationship. That 40+ yo 5th boss may is politically naive, but he knows his limits in love and tolerance.