in my opinion it's easier to learn japanese

my major is Korean and I think it's easier to learn Korean because the Japanese characters are more difficult and also grammers

Maybe Japanese. Japanse is easy to pronounce. But, 南 is pronounced as 'nā' in Chinese(Mandarin). In Japanese, it is pronounced as 'Minami(みなみ)', also 'nan'. This means you have to pick up two pronunciations mostly whenever you learn a Japanese word. And the Japanese use traditional Chinese characters and speak in various reverant language. And Japanese grammer is not easy. This is why I don't think Japanese is really easier than Korean. There is just relative difficulty between Japanese and Korean.