This is really immature on Kotoka's part.. So you are allowed to have a fetish, but Tatsu isn't? You can easily test his love for you by cutting your hair.. Not like he can just cut his back to see if you really love him over his 'back'..
Edit: If I were Tatsu, I'd be crazy angry at the unfair and childish behavior Kotoka has just displayed, especially after Tatsu called her an adult just few chapters back. He should put off proposing to her (if not completely break off with her) seeing as how she still doesn't believe him, and I stress again, is using a method to test him which he himself can't use