When checking to see how you got that I only came across Kapampangan, which is Philippines. It’s possible it could mean that in something else, but I assumed most people remember that Emi is Japanese, and of course her family is heavily rooted in Japan. (If you dont want to read all this – skip to the ending paragraph!) Being a weeb- I know that Big Brother and Older Brother comes in many flavors, Onii-san (Onii-chan), Niisan, and Aniki. From what I understand, some of these terms change based on family relation (younger addressing older, sister to brother or brother to brother), closeness (Ani with ki added is seen as “vulgar” but i think it is roughly like calling your sibling ‘bro’), and formality (Onii-san being more respectful).
In Japanese, Koya has several translations, most commonly I see “shack” or “Small house” however, Japanese names have some oddities to them that I don’t know everything about them. I know that there are many “old names” that have changed meanings, and even some names that are said the same- but because they are written with different Kanji they have totally different meanings. So to break it down Ko can mean little, but there is another kanji used that is also pronounced Ko, and it is- a shorthand for happiness? It’s hard for me to explain it because- while I can see it online, I don’t have all the context. I don’t know if thats an old shorthand, if you should even call it shorthand, if its something “new” or something very old. All in all, it seems that to truly understand a Japanese name, you have to see how it is spelled, or have its origin explained. Otherwise you end up with the cliche in anime- where people make fun of someones name because it means X (which is something silly or lame) but the way it is spelled actually means Y – which is something cool and respectful. A relatively recent example of this is Izuku Midoriya, who is given the nickname “Deku” which generally means- wooden doll. As an insult it basically means, dumb, block head, something like that. Yet, it can also mean something like “the start of a story” based on the spelling. It can also be seen as a blank slate. So while most people see it as something like “block head” he is determined to see it as his new beginning, and or – that he is a blank slate, ready to be molded into the next great hero.

Japanese is complex, but- if you want to know where Koya came from for Emi- Emi’s name means Blessed/Beautiful. Her last name is a name that also translates to – A clever and quick witted leader. I have no idea what the Kanji looks like for either of that so if I dared to try- I might end up calling her “Reflect – Little animal pen” (not a joke- Koya can also mean animal pen- part of the Kanji used in Koya roughly means little even though its describing the building/pen size- it’s weird)