Hero and heroine have a painfull past and might have met at a school as children..
The second female lead is an adorable person who makes an U-turn from being a noisy and terrible ex to the main hero to a great supportive person to the female lead.

In both the main hero is in search for the heroine half of his life.. At first then met by an accident. When he suspect he found her.. he treat the heroine well.. Then he think he made a mistake..., but even so.. fall in love with the heroine.
In both the main hero is very cold and stingy with money at the start, but no so much at the end.

A male chef tries his best to appeas to the culinary needs of his customers. Both are chefs which are very skilled and both shows reveal the reason the particular customer requested the said dish.

It's about how troublesome could be to try to live as a normal citizen if you were born or made yourself an outcast of it. It's about thing to have a personal growt. It's about one young woman trying to help/implement that growth into others and the helplessness she feels if/when she doesn't win that battle.

Both are dramas with female leads which are cute, fragile ladies with glasses on a noble government position which are trying to straighten up a social outcast by trying to solve some of their problems. The main difference is that in Gokusen the heroine uses martial arts to scare of the people, which are trying to hurt the people she is trying to protect... In Zenkamono the heroine is left alone with the system.

Both are a female leads slice of dramas which operates with the daily work and life condition of a person. Danda Rin is about work conditions and Zenkamono is about people on probation.
Both are very inspiring dramas that shed lights on the importance of those people's jobs.

Both have as a main plot the media and it's influence on the people's opinions + the responsibility of the ones involved in publishing (redacting) a certain topics and news. Both shows are somewhat slice-of-life and involve 3 main protagonists with the same gender (but different in both dramas) who work in the same field, but which view on their work isn't exactly the same... While one focuses on popularity and money.. another focuses on the truth and responsibility...
It also involve the 3 protagonists love stories and live.

Both have as a subplot a case of an accident that might be responsible for the death of one of the protagonist's parents death and involves a corrupt make polition and his son.

A woman is in a love interest with two different man: the first one has a psychopatic tendencies and is responsible for her father's past sufferings (could also be responsible for his death in the present).. and the other is a loud and good-natured, but oddly naive being who has been emotionally separated by his actually loving family. Both of those lovebke oddballs have a their mother dying on an early age and their father remarrying to another woman. They have another sibling through that marriage.. the female protagonist is an only child.

In both the main male protagonist is an only child who managed to accomplish his childhood dream (which was in one of the cases astronomy and in the other architecture), but failed in another aspect of his life (whether his health or his wealth). After this happened to him his childhood crush and later on fiance dumps.
In both the main heroine hhin't somebody unknown for the guy, but instead she ahad a crush on him sincee high school, but he was then very popular and with a girlfriend, so she chose to keep some distance from him. She is in both cases a very shy person who confront people when get angry, but even so sometimes taken on a lot of blame, which isn't hers.

Both are romances with a big age gap between a male and a female. In both the male is older one.
Both have as a main hero a loner, who lives a lonely life even though he doesn't have any money issues. A person who only wears dark colours and lives for his work (which he regards as the mission of his life) and has established part of his past life in a foreign country (which is in one of the dramas Neitherlands and in the other Canada). In both he shares a house with another male, whom the female lead almost befriends... Both have many flashbacks about his past.
In both the female lead is somebody, continuing her study, who he encounter by chance. The female is the person who finds him first due to a misunderstanding.

Both have the opposite attracts romantic comedy mixed with a bit of a catch-the-cultprit/murder-mistery.
While the genders in both hero and heroine are reversed they involve one main lead, which is calm, seemingly mature and well-educated person and another one, which is loud and lacks basic culture. Surprisingly they both make great couples.
Both leads (genders reversed) are surprisingly successful in their work even though their lack of education and do it from a long time so that they help their family.