Female lead goes undercover in the mob world and reunites with her past teen love while there. Struggles with completing her mission due to previous personal feelings reigniting.

Mobster male leads, male and female leads have past childhood/teen connection. My Sweet Mobster is heavily comedic with occasional serious undertones, Fatal Allure is solely serious and often reads as a soap opera.

Mobster male lead unexpectedly falls in love with country-type girl. Kang Koo's female lead has a child, Lovers' female lead has kid siblings, etc..

Mobster male lead, quirky & poor female lead. Relationship starts off on chaotic misunderstandings and the leads can't stop running into each other despite disliking each other from the start. Romcom atmosphere, etc..

Two of the goofiest most adorable and wholey loveable female leads I've seen in K-dramas. Both are on the poorer side and are gold-diggerish (in a relatable way), while the male leads are rich and stern.

Both feature parents who disapprove of their child dating the other nationality. Go's female lead's parents don't like Koreans, Friends' male lead's parents don't like him dating a Japanese woman.

Relationship begins the same here, female lead is robbed and follows male lead around aimlessly for help. Plots diverge soon after but I noticed the parallel and couldn't help but compare!

(reccing this as of episode 2 of Doubt airing)
Both feature an arc regarding a child killing a child now grown up, and the mystery of if they are capable of doing so again in adulthood. There is the push and pull of the perpetrator's family wanting to trust believe and understand them, but ultimately not being able to let go of that suspicion.
Both the killers have a stoic and unremorseful personality assisting in the struggle to accept them and their words.

Dong Jae being the spin-off of Stranger, I would suggest watching seasons 1&2 of Stranger first to get a good grasp on his character.

Both center around crime investigative fathers who have strained relationships with their teen daughters. Working on cases that they soon discover their daughter is involved in, they work to hide certain details to protect them while simultaneously searching for the truth.

Gender swapped but very similar story for the most part- rich main character loses memory in an accident and starts to live with other main character while they recuperate (creating messes and causing trouble while doing so). Male leads are both harbouring secrets from the female leads, romcom atmosphere, etc..

Both follow an office-working female lead meeting and later convincing an everyday street-smart type of guy to have a fake relationship with her.