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Jesotku: In a World, were an average person has the looks of someone like a Supermodel or the K-Pop artist (post plastic surgery) on Earth, obviously someone with normal features would look ugly to them, to even compare that person to a Kobold.
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SingLove: I don't think Makoto and Shiki were talking in Monster Language (they were either talking telepathically or some ancient language). Remember, because of the Goddess Blessing, Makoto can speak in all languages except the Common Language of the Hyuman.
Also, these students are from a big city, and from probably some Noble house, so they probably never had heard any Monster Language yet, unlike previous people who worked as Adventurer's so had come across Monster, to know the difference.
As for the less focus on MC's looks, i think there was a reason for that stated in the WN (not sure as its been quite a while since i read the WN).