Ace is your big brother, he is very protective of you since his little brother and your big brother Sabo died, he made the promise to be always be there for you and to never die

Ace and you get trained by your grandpa Garp. Learning armament and observation haki at a young age. And even finding out you 2 have conqueror's Haki

Garp: you 2 are Amazing! you 2 will become great marines! Just like me!

Ace: no! We will be Pirates!

as they argue you find a strange fruit, the Mera Mera no mi