Rain or Shine

Both series tell the love story (with a strong physical attraction component) between two people who carry many wounds and traumas from the past. Both female leads have suffered in the past and continue to suffer in the present because of their families, albeit for different reasons. Both male leads wear a tough exterior to hide the deep pain they carry inside. Neither series is a rom-com, even though the promotional image or the beginning of Me Too Flower might suggest otherwise. Both are melodramas.
There are very meaningful and deep dialogues in these series. There is sadness but also some really cute, cozy moments.

Both ML and FL suffer/have suffered loss or trauma. Both heal and slowly move forward with each others' help. The tone was similar in many ways.

Here's My Plan has more dark humor while JBL is more soft/melo, but they both have a slice of life feel and show characters dealing with difficult life and family circumstances.

Both leads have suffered loss or trauma and are distanced/cut off from society. The ML has a history of getting into fights. Both have a melancholy tone with a theme of slowly healing.

Both follow people going through spells of depression and tiredness of life as they try to worl through their issues

Similar slice-of-life feels and romance
Romance is slow, steady and understanding (super cute)
Very cute and slightly immature/childish male adults with mature, empathetic and tsundere-like female leads

.............................In both drama characters are introvert and some how it reveals same feeling.................................................

- realistic and flawed characters
- slow-paced romance
- angst and heartache
- love rectangles
- bad parents

Having mentioned this by a couple of users in the comment section, I agree that they are similar in certain ways. Even though The One and Only just have released 2 episodes, I can already similarities in the main couple. They are both scarred by their traumatic childhood that heavily influenced their present lives. In JBL, it seems that the main leads are positively influenced by their childhood (like how they chose their career) but I can not say the same for the couple in The One and Only.

Very different plots, similar characters/main relationship. Both dramas have two lonely, poor, and damaged leads - a FL struggling with issues with her family and an orphan ML who works hard jobs - who become each others' family.

Not your typical love story.A realistic drama about the hardships and struggles in life. A great storyline about finding true love. A must see for everyone who wants tearjerker dramas.A plausible performance from the actors and actresses. I just loved everything about it.It shows the real meaning of love and family.

Mad for each other seems more like a comedy at the beginning but gets more serious as the show progresses. Just Between Lovers is more melodramatic. Both shows have a love story about healing and people struggling with mental health issues. JBL shows PTSD and alcoholism while MFEO shows anger management issues, paranoia, PTSD and social anxiety.

SPOILER ALERT
In both the shows the couple has experienced an accident together in their pasts.
Though the plot in both shows is different they do have a bit similar feel

After receiving a terminal diagnosis, a devoted husband discovers his wife’s affair. With little time left and his son’s future at stake, he embarks on a relentless quest for revenge that will change their family forever.

both Black Dog and Just Between Lovers are similar in their slow and healing nature, both had that cold blue vibes