Hey!
First of all, I am sorry to hear you got rejected this time around. I would absolutely encourage you to try again.
If you go back to the MEXT thread for 2017, you will see two members in particular who were on their THIRD time applying that year - and both got accepted! I believe both were active in the previous year's thread for MEXT as well. When I went for my interview, one of the other applicants there was on his second try.
There are many factors that can attribute to being rejected, like the proposal, language level, quota/budget, that year's competition, etc. What matters when you reapply are the ones you can control. Rework your research proposal and study the language over the course of this year. I can only speak from my experience, but I think I won the spot at my consulate because my research pertained to something very specific that was happening within the next two years in Japan in my field. I was just talking to someone the other day whose friend is in Japan on MEXT studying gender studies through visual kei. A popular YouTuber who talks about MEXT describes her winning research proposal as being focused on business start-ups surrounding the Tokyo Olympics.