Increasing
Go from a bow to a small gun and you're increasing in fire power! Even though the gun is small, it's still a step up from a bow.
Imagine increasing your power with a new weapon. What would it be?
び, み
や
None
You keep trading in weapons to get increasingly stronger gear, when you realize that at the top of the list is... a Yankee's (や) baseball bat? Huh. I would have gone for a tank or a bazooka. But I guess if this will increase your power level, you have to go for it.
Imagine walking down a line of weapons, each one increasing in power from the one before it. Bow, small gun, bigger gun, tank, Yankee's bat. Yup, that sounds right.