Trouble With Vanitas' Sentiment

Even though I'm leveling up a lot with the characters, I still can't beat Vanitas' Sentiment, he really is harder than the Lingering Sentiment from Kingdom Hearts 2 Final Mix. I need a strategy to beat him, I die in like a minute. I will think of a strategy and see if it will work. I see lots of people on YouTube beat him using the same attack over and over again, and I see other people using different types of attacks, I don't know which I should do. Even after I beat him the first time, I think you can fight him again as much as you want. Once I beat him, I then have to get ready to fight the Mysterious Figure, which is the new boss included in the international release of the game, and then included in the Japanese exclusive Final Mix release. I put an image of Vanitas' Sentiment below, along with an image of the normal Vanitas. Vanitas is the first one below, and Vanitas' Sentiment is the second one, you will definitely see the difference between the two.