A New Pet Bird.

All of the ring guardians have an animal box weapon that is also their companion, in fact most characters in the series at this point do. Yamamoto's box weapon doesn't have a name for it like some characters do however it is extremely powerful. Yamamoto's box animal is a swallow. Why? Well, in theory the box weapons are supposed to represent something about the character.

Swallows are incredibly personable animals. Many are encouraged to live around people. They are also deeply saturated in history. Swallows have been considered to be very religious and some legends mention them in the bible or the quran as well as in ancient greco-roman legends. Swallows are fast fliers and extremely streamlined birds. They could be compared to the speed and accuracy of a sword strike. They also have great endurance. Swallows have pointed wings and have short bills with strong jaws. Swallows are also known to be very social birds they usually live in groups, though some live alone in territories. They protect each other by living in groups.

Overall, I suppose Yamamoto's box animal isn't the most obvious in relation to him as a character however both the swallow's physical characteristics and way of life to fit Yamamoto. As I said before the way they streamline their bodies while flying is much like a sword. Also the way they carry themselves makes them look long and lithe, much like Yamamoto's build. Yamamoto is also a very social person and while he can fight alone he protects his family, friends, and his close social group very fiercely.