A lot of the Kiss X Sis episodes flow much in the way you'd expect long anime series to. They tackle different scenarios and situations while progressing through the main story. Early on during the OVA, Keita found himself depressed because of frustration and the pressure that his classmates and studies were giving him. His two twin sisters' were concerned for him (both as a sibling and as a romantic interest), and treated him to a Christmas celebration away from home and his books.
Right off the bat, we see a significant change in terms of costumes. Though Keita didn't opt to wear anything Christmas-related, both Ako and Riko wear Christmas costumes for their night out. Both are dressed in Santa costumes with slight differences between both. They also chose to go out for karaoke which is a popular thing to do to in Japan during the holidays. Even the usual opening and intro were changed slightly to reflect Ako and Riko's Christmas costumes. It's simple, but the small touches makes a significant difference to viewers and those awaiting fanservice.
Culture and Activities
As you might have noticed, the episode is a great reflection of Japanese culture, and can also give you an idea on what to do during Christmas. Karaoke is a popular option and you'll find that a lot of Karaoke bars and places are full during holidays and weekends. It is a popular trend not just in Japan, but in all of Asia. If you don't have a karaoke place near you, you can purchase a karaoke machine, which can be an investment for future events. Even the internet can be a popular place for one's karaoke needs, though of course you might need a microphone for that. During this Kiss x Sis episode, the three reserve a karaoke room and also ordered some oolong tea, a popular drink in Japan.
A Kiss X Sis Twist
Of course it wouldn't be a Kiss X Sis episode without the ecchi. The trio soon find themselves with an alcoholic brand of Oolong Tea given to them by accident. This event will soon later dictate their actions as it reveals quite a bit about their drunken habits. Riko is easily knocked out by alcohol and while Ako is your typical drinker, Keita reveals a more perverted side to him if he gets too drunk. Action starts when Riko needs to pee and forces Keita to escort her to the restroom. This continues later on in the karaoke room when Riko's asleep and drunk Keita is left alone with Ako.
I won't spoil the rest of this episode- you'll have to see for yourself what happens. If you're into the series (and the ecchi of course), put it in your lineup for holiday-themed episodes to watch! Hopefully we also see new Christmas specials from this season's anime as well!