Loafy dw too much I think whichever you choose will be a wonderful experience for you in my message I talked about lots of bad stuff but that's because I'm a bit of a pessimist 😅. Yokohama it's a nice place it's outside of Tokyo so its quieter but still very city like and it's a 40 minute distance from Tokyo. Thinking of the kpop aspect Japan is pretty nice cus they still do lots of popups and concerts there, you can go to Shibuya tower records to buy K-pop merch I went there it's super cool they have a floor for every different genre of music and most kpop albums come with pobs special of that store. And Japan can be expensive but there's a lot of good thrift stores from books to clothes you can find things in perfect condition for just 100 yen. Also If u go in an exchange program it's likely there will be other exchange students you can make friends with and honestly who wouldn't want to be friends with you🤭 🌸

Omg Loafy that's so nice!! I'm also planning to get a scholarship for Japan next year. I don't think I can offer an opinion as thorough as Cain but I'll try my best. Firstly I will recommend you to look into the way that your major or study field is taught in each country. Because I'm an art student I know there's amazing opportunities for learning on that field but in Japan it's a super competitive field there's only one public university of arts in Tokyo.

Personally I'm more knowledgeable about Japan so I can tell you more about them. Firstly they're actually kind of racist but in a way they don't realize it's wrong, they're all super polite and kind all the time but it's not uncommon to find restaurants that don't accept foreigners or even If you speak perfect japanese they will behave like they don't understand it. People born there with mixed-race backgrounds often face significant discrimination throughout their lives. This behavior is less common in Tokyo but even then most people won't speak a word of English so you'll have to really practice the language.
I do know that in Corea they offer more courses in English. Another thing I think might bother you is that in Japan is very hard to make friends most people are polite but they won't go out of there way to make friends. It's easier to befriend other foreigners there than the locals, that said I've seen people in university have it easier making friends but a lot say they're usually superficial level friends. From my perspective people in Corea especially uni student are much more social and outgoing so it's easier to make friends. Corean universities also have lots of fun activities you have probably noticed but they do student festivals where they invite K-pop artist, at least that's the case of the most prestigious universities.
On another aspect Japan offers more work opportunities be it a half time job while you study or a formal job after you graduate that said their work culture is very toxic and demanding but I know a girl from where I from that got offered a job for animation in Tokyo after studying there, she worked there for a while but now she freelances for anime studios from her country. In cost of living Tokyo is super expensive so I'll recommend you check if there are student housing options, that said it's really easy to live on 7/11 food and really tasty also :) The subway there is quite efficient and always on time it's cheap too I don't really know much about the Korean subway though. In general both countries are very safe, except for women lol, in Korea is more a social aspect of how women are perceive in a more.. traditional way per say but in Japan there's a lot of pervert and sexual harassers and the police won't do anything about them most of the time.
Another thing is that if you are a picky eater like me you should think about the food I don't like spicy food so most of corean dishes are a no for me😅. Now there a million more tiny things I could say but like Cain said I think it's important to do your own research I recommend you analize it firstly in a more analytical perspective, how much would it cost, do they offer you a place to live, what about food or clothes would you need a part time job etc.. and then you can see it from a more people based experience, watch blogs about people who have a studied abroad or live there and look not only for the nice ones but also that bad experiences so you can have a look at both the pros and the cons of each country and then you can contrast them to see which is a better fit for you. Hope this helps sorry if there are lots of mistakes 🌸