Thirty but Seventeen (2018)

Both stories have different plots but they have same feel. Both lead girls are cute and lively with and introverted male lead.

Similiarity:
- Both female lead has mentality of teenager due an accident.
- Both female lead has a teenager crush on them.
- The main lead are lovable! (ofc)

Even tho it has different kind of plot, but both are interesting to watch

In both dramas the FL moves in the ML house. Both main couples have their differences in the beginning but then the path to love begins...???? The ML helps out the FL when she needs it :)

Both dramas deal with the pain of loss and emotional struggles. Both have such a sweet but gradual love story. Both are so pleasing to watch. Both have an overpass that holds significant meaning. Both have wonderful supporting casts that support the main characters.

not very much similar, but both dramas have very healthy positive and funny vibe (though Fantastic touches very negative subject and has sad parts it still manages to be positive drama), realistic relationships and characters, multi characters and still quite 3d all of them, without unrealistic villains (though Fantastic has very pad people as one family but still realistic ones), primitive cliches, healing...
there are no annoying love triangles, I mean it is in both drama but very healthy when SML and FL are reall good friends without broken hearts.

both are really good dramas, with one look not some new or extraordinary plot but really good watch, dramas that enjoy you (and I's saying it when 80% dramas are boring for me after 5-6 episode)

A show about growing up. A girl is unable to fully experience growing up due to a sad circumstance but now has the chance to experience her teenage years at the ripe old age of 30.

FL characters in both dramas come back to a house their father built brick by brick after being forced to vacate the house due to circumstances beyond their control.

30 But 17 has almost the same free-spirited, adorkable vibes. Antisocial ML and FL who is a 17 year old stuck in a 30 year old's body. It has the same light feeling throughout.

Similar setting, with the ML's house acting as a sort of "base" for the rest of the cast to be one big happy family. Because of all these crazy characters, ML thaws out and it's all so cute. The cast is made up of brilliant actors, just like this one - lots of them are seriously popular now - Shin Hye Sun as the FL... Lee Do Hyun(supporting character) and Ahn Hyo Seop(SML) are still young babies in this ??. And the housekeeper, Jennifer, is one of THE most iconic characters in Kdramaland. one of the best drama endings ever.

Both male leads are a chance to correct their mistakes and the love for their wives is rekindled, becoming more stronger than before.

both dramas are different genres but the FLs both play the violin and encounter hardships trying to make their dreams a reality

Both have a male lead that faces a trauma leading to him becoming more reserved. Through the help of the female lead, the male lead becomes more extroverted.

They aren't really similar in the feels as Welcome to Waikiki is much funnier, but they are both lovable and feel good. They both are similar in the found family aspect with all the characters being unique and weird in their on way. Thirty but Seventeen has some very funny moments too yet also sometimes makes you want to cry. Just a little but you have been warned.

Both hilarious romantic comedies involving main characters with shared childhood traumas. Both couples don't initially know that that they had met when they were younger much less shared life changing moments with each other. Both great romances though WWWSK is much more mature and 30b17 more innocent due to the characters' emotional ages.

Both shows have very memorable characters and love stories with amazing acting. Both shows have hilariously quirky characters who are housemates, male leads with severe PTSD who find healing through his housemates and especially the female leads. Both couples have amazing chemistry in their own way though IOTL is much more mature and 30b17 is much more innocent due to their emotional ages. Both shows openly talk about going to seek psychiatric help which is very tabooed or rarely shown or talked about in Korean or Asian shows at the time of their airing.

Both are written by the same writer with similar genre of romantic comedy. Both have Shin Hye Sun in it which show how amazingly far she's come from being a support character in one show and the main lead in the other. Also it shows her range as both characters could not be more different. Both male leads have PTSD that often interfere with their lives and the love of someone from their childhood who they didn't recognize initially brings them both out of their hard shells to help them return to who they were when they were younger. Both shows have great moments of Womance though in 30b17 the women are not love rivals. Both have a lot of humor and heart.