i don't write official ages out normally but yes, shu is in his late 30s-early 40s! i wanted to leave it vague but i imagine him in that age range, make him whatever you wish. he's not super old but he's established enough in the art school/has had enough experience to get tenure and stay comfortable in his job/social standing.

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as to mika's age preference, i think he prefers people similar in age to him, because of several reasons:

• one is simply vanity. he mainly thinks that the most entertaining and visually-pleasing victims to the camera are people in their 20s like him, especially for viewers looking for those kinds of things and willing to wire him money. for someone with very loose, questionable morals, i do think he has a strong preference against anyone younger than 18, and anyone older than 30 that may have a family of their own. there's also an important keyword when regarding shu: that he is LIKELY outside of mika's age preference. he's willing to bend on that age preference if his instinct tells him it wouldn't get him nailed or the victim wouldn't get away easily. sometimes he intentionally skews it so he doesn't get too stuck in a pattern that can make him easy to trap. and mika is someone to rely on his instincts that have gotten him this far. he is however, VERY prone to becoming overwhelmed with emotion like rage and spite.
• another one, as i've implied in some of my tweets and posts around awoa that i'm elaborating on, is also because of his cannibalistic desires. generally he prefers people that don't do drugs recreationally (to his knowledge), are somewhat fit/have some qualities he may want for show, and are generally independent. he ideally wants people that wouldn't easily be missed, but sometimes it doesn't happen. he may have started off with low-risk victims but found they don't really taste all that well when he began experimenting, and elevated to people considered medium-risk in order to satisfy his own needs better--people that go out at night on walks/drives by themselves, lone travellers from another country/area, etc... mika has to already go through an large amount of effort to make sure they're subdued and unable to leave his work area, he can't leave a trace of his behind, and he will not stalk someone unless he's ABSOLUTELY set on making them his next target and will not be able to rest until they're on his plate. my guy has school the next morning and he rarely misses, just to keep up appearances. he kind of already seems a little off-putting when you spend more time around him, but he does have friends that would notice if he was gone for weeks at a time and he has a more unassuming exterior in public. he is attractive and blends into his environment naturally/isn't easily noticed, which is why he's able to lure people without raising much of an alarm

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i hope this makes sense, i know its a somewhat convoluted explanation.. i enjoy character analysis with a side of erotica and serial cannibalism