While in itself being quite different ( Mermaid mystery vs. BL drama) they both share a plot of reincarnation and rediscovering the past memories and the hidden conspiracies around their past selves. I really love both of them a lot and rewatched them several times. If you are looking for something fresh and fluffy, check them out!
I think first of all the obvious similarities stand out: The gamer relationship between two people. Both couples get involved with each other through some coincidences and end up falling in love. Further than that, I would like to note that the leads are really good fits for each other. (Almost) no annoying misunderstandings, and if, they get resolved rather quickly. The MCs show great understanding of each other and fall in love pretty early on and more so try to stand up against outer dangers together. They are really fluffy and calm. The FLs are pretty similar on their own, too. Calm, smart, talented in their field. They don't need a man to help them at all. They have quite healthy relationships. Overall the dramas just give out very similar vibes and are an easy watch, if you need a good old romance without too much angst or second-lead drama.
While they are quite different, at the core they both share the 'Trapped in a story'- plot. While the FL in Extraordinary You gains self-awareness of being in a comic book, the FL in TRoTaR is an author suddenly waking up as a character in her own story. Both FLs are side-characters that are bound to die but try to change their fate while also experiencing and somewhat unexpected romance.
In both dramas, the leads are connected trough their past but do not know at first. While in It's Okay to Not Be Okay one of the main leads is calm and the other one quite hot-headed, the dynamic of the couple in Thirty but Seventeen is more of a calm ML/ naive FL one. But in no way is it annoying or cliché, do not misunderstand. What they have in common though is that both couples support each other with their internal struggles of trauma. I think both MCs have great chemistry and the storylines are far from cliché or boring. They explore more unique situations and there is never any annoying doubt or misunderstanding between the leads. (At least as far as I remember; it has been a while since I've watched Thirty But Seventeen.) But I think if your taste is similar to mine, you will enjoy both dramas to a similar degree!
Both dramas' plots revolve around a couple that is entangled in time travel and mystery. I enjoyed both dramas a lot! Acting, storytelling and character development is superb. Both have melodramatic but also comedic moments.
