Okay okay okay okay. First, vahki are robots that have no differences. Even though bohrok are av-matoran, they have no gender after transformation as they are robots and have no differences like matoran between individuals that could symbolize other genders, such as voice, body-type, etc. The krana also have no gender as they don't reproduce biologically (an object is put in liquid, wow which makes biological gender non-existent) and don't have any of the previously mentioned things or the sentience to identify as anything. Kraata go the same way as they are created by makuta. Though, a more sentient or mutant rahkshi, would most likely be male. Only because Kraata-Kal is usually regarded as a he, and male seems to be the default gender as all the piraka, most of the matoran, barraki, are male. Visorak have genders. I think everyone agrees.