One Piece: Kenshin's Journey

The story takes place 10 years before straw hat Luffy sets out on his adventure. Kenshin, our protagonist who is always befriending other pirates and is planning to create a grand fleet seems to have an interesting back story. What is it? Where does he come from? Why does he want to amass such a huge army and why is he so fixated on the year 1524? What will happen during that year? No one knows.