I don't think changing the subject of the conversation from military units in the samurai manga Otonashi offered to lend to Takasugi, to Power Rangers, really helps with translating the joke when you're making the change to use the word "formation" as a misunderstanding for "position." Just as easily could have invented something related to the samurai manga like "I love the different uniforms they have for each (military) position. Hey, if you had to choose one, which position do you like best?"
Or if you want to go really out of pocket,
"If you could join one, which unit would you like to be put in?"
"WHICH WAY DO YOU WANT TO PUT THE UNIT IN?!"