Those are extras which varies with content - it might be more BTS, side story, epilogue, some steamy scenes, which didn't make to the title, sme content around special occasions like Valentines, Christmas etc. Overall like some extra content, which didn't make it to the drama or steamy one for the pure fanservice, or filling some gaps from the original story, or BTS one. Which one is here, dunno :P
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https://kisskh.at/search?q=extra&adv=titles&ty=83&co=2&so=relevance
Those are extras which varies with content - it might be more BTS, side story, epilogue, some steamy scenes, which didn't make to the title, sme content around special occasions like Valentines, Christmas etc. Overall like some extra content, which didn't make it to the drama or steamy one for the pure fanservice, or filling some gaps from the original story, or BTS one. Which one is here, dunno :P