-both male leads suddenly find out they have a child, they didn't knew about
-both ML have no idea on parenting
-both FLs help MLs in parenting MLs child.
Both are about grown men around their 40s who suddenly find themselves having to take care of a teenager. They are forced to grow up and mature in order to do so as well as navigate through the hurdles of their own lives. Old Boy is more of a slice of life. Both dramas have a similar vibe.