Danna-san ("Boss" in the English translation) was the leader of the Cross Guard that defeated the Chess Pieces in the war six years before Ginta's arrival to Mar Heaven. Even though he came from another world, the world Ginta came from, he loved Mar Heaven, and was more than willing to fight to protect it. He died in battle against Phantom, the immortal military leader of the Chess Pieces.
It's later revealed that Danna-san was actually Ginta's father, who disappeared six years prior. Apparently, he acted the exact same way Ginta does, which makes a lot of people have high expectations of Ginta.