Asako steadily becoming more butch and/or assertive
She's not really going the butch route, she's incredibly feminine. Butch may be seen as a masculine form of gender expression, but that doesn't necessarily mean you're assertive or even the "dominant" one in the relationship and appearance plays a huge part in it, it's beyond tomboy level. People who choose not to shave (body or facial hair), who get masculine haircuts (long or short), who dress like the men in their culture is expected to... It's a much more extreme rejection of femininity.
Incredibly cute chapter! Her smile in this page is seriously so cute. Just something really nice about how casual they are about all that's happening so far.