Your build. You're clearly an athlete of sorts and seeing how... Haru was it? Knowing you were connected to him made that easy to decipher. Your technique can bee seen in your back and shoulders where the muscles are especially defined. You also have extremely tonned arms, but there is a slight tenseness in the rotator cuff muscles which suggests you use that part of your body often, and in this case, to propell yourself through the water.
As for personality, backstroke is generally more open and one can see the swimmer's face while they do this. Free style is more closed, but with far less restriction. [Holds a hand up] Granted I have a limited understanding on the subject, but just from what I do know of it and the small interactions I have observed with your friend... It seems your styles are good for each of you and compliment who you are as individuals.