They were developed to hunt big prey like wild boar and bears. Helen Keller was inspired by the Akita's loyalty and bravery, and brought the first few Akita back to the US. Military people serving in World War Two also were impressed by the Akita and brought the dogs home with them.
Akitas require a skilled and devoted owner. Their power and tendency towards dominance with other dogs, as well as their strong guarding instincts and independent nature, can make them difficult for a novice dog owner to handle. That said, your Akita is an extremely intelligent and adaptable dog capable of learning new ways of doing things, even late into life.
If your Akita is showing guarding behavior around you on walks or when visitors come to your house, but is behaved with visitors and strangers once introduced, you need only give your Akita instruction in how and when guarding is appropriate.
Akitas tend towards aggression with same-sex dogs and dominance in with dogs in general. There may be a limit to how much restraint you can expect from your Akita, so be realistic in your training goals.
Learn what motivates your Akita. Find a food that has a smell that will distract her from whatever she is focused on, or see if she loves tug enough to play instead of behaving aggressively. If your Akita has very strong guarding instincts, you may have more success teaching her when to be aggressive than overcoming aggression altogether.