I’m not sure if it’s possible to become fluent on the level of a native speaker in 6 months unless you have some amazing ability to pick up language. However, you can learn enough to be conversational and get around in Japan by yourself.
I’d say definitely go live in Japan for 6 months while forcing yourself to use the language as much as possible. It won’t help you much if you live in Japan but still watch videos and read content in you’re native tounge.
However, first and formost! You should start by learning Hiragana and Katana with some simple Kanji here and there. Also learn basic grammar rules and vocabulary so you know what you’re listening to.
Last and actually most important! Make friends with Japanese people. Some of them may also be interested in your culture and language and may want to talk to you as well. Don’t be shy, but don’t be obnoxious either. People in Japan don’t usually like being accosted by foreigners to be practiced on, so just be respectful and you should be fine. That’s why friends are the way to go. If you’re in college or are thinking about attending, definitely look into a study abroad program. It’s worth it!