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The main page gives the "Toy Ship" trope, saying that that "Nabi and Doki are young teenagers at the most." I don't believe this is so. It is pretty obvious that they both live alone, some of their friends are clearly adults (e.g. Hana, who manages a band and has a bodyguard), and they don't act like "young teenagers". Young adults, maybe. Like, early twenties.
Also, just to support the possibility that Il-ho is Doki's brother — the part where she puts him in a nelson may have been a sibling rivalry thing (I don't see any other explanation for her doing that, especially when they barely knew each other if you assume he's not her brother, and especially considering that she beamed at him and greeted him like a friend before putting him in a nelson). His blushing afterward, and Sam-ho's subsequent "smirking", may have been more of a "hah your sister just owned you" rather than a "hah you like her" thing.
For the second part it might not even be for a sister reason; more like "Hah you got beaten up by a girl"
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How well does it match the trope?