I don't watch a lot of Korean dramas as I tend to drop even the popular ones like King The Land, My Sweet Mobster, and My Demon (at least I watch half of this for Song Kang's visual not like the previous two which I dropped after 1 or 2 episodes). Kind of avoid them now except for my favorite actors' works. So I'm lacking knowledge but here are some I recommend based on the five titles:
From the description of my colleague, seems like Another Miss Oh (which I love and I even memorized the OST) has some similarities with Mr. Plankton (which I don't ptw) since FL starts a new relationship with ML after a cancelled wedding (for different reason but still I feel it quite similar and both ML at one point are about to die just in AMO the ML ends up alive).
Twinkling Watermelon is a bit similar to Twenty Five, Twenty One in terms of youngsters' friendship and romance, but I see you dislike it. So maybe... Tale of Nine Tailed 1938. Both are about friendship, changing past for a better future, mending relationships, and some romance and unrequited love between leads.
I see that you've been watching My ID is a Gangnam Beauty (which I love, and I find its manhwa is better than the True Beauty's) so maybe Oh My Venus as they both about makeover, fight againts low confidence, and newfound romance.
No one's around me watching Revenge of Others so I'm not sure.
18 again have some similarities with Go Back Couple, it's just the two leads back to the past, but both are about mending a couple's relationship. And maybe Thirty but Seventeen, it has more angsts since ML is feeling guilty and traumatic the whole time about bus incident, but imo has some similarities with 18 again. For example: regretful and remorseful ML, younger man approaching FL, ML want to make amends for FL.
