Now in Japan there always seems to be male and female days. Whereas in the west Valentines day is where couples give each other gifts, in Japan only men get gifts on Valentines day, but a month later is White day where the men give the ladies a gift in return. The same is for the Children there is the Dolls festival for the girls (on the 5th of March see http://www.pbase.com/jameslclarke/image/111286709) and then the Carp Festival for the boys on the 5th of May. The funny thing is that 5th of May is also a public holiday called “Children's Day” whereas there is no public holiday on the 5th of March.
So the question is do we as Christians fly Koi Carps for our sons? There are some groups who would avoid doing this. However we must remember that many of our so called “Christian” Holidays have pagan origins (like “Christmas” and “Easter”). I think as long you are not worshipping another god, and the you place the focus of the holiday is on Jesus then it's OK to celebrate them. At the same time I think we can go without these holidays and still be just as good Christians, but these holidays are good bridges to connect with other people in the world and share the Gospel with them. When I was in Singapore the church I attended there used to celebrate the “Holy Ghost Festival” as Christian version of the “Hungry Ghost Festival”, and it was a time of a lot of evangelism and it connected with people there. The church I attended in Bangkok has it's own ways of celebrating Songkran Festival and Helping the Elderly (rather than praying to ancestors).
It all comes down to contextualisation rather than syncretism. Contextualisation is adapting our method of presentation, but not the core message, to fit a cultural context. Syncretism is where we mix our ideas with other cultures ideas to come up with something acceptable to the culture. So contextualisation is the right approach, syncretism is the wrong one.
So, a contextualised carp festival, might be through drawing parallels with some of the perceived virtues of of the carp with Christian values. Maybe rather than a journey to the mountain to be come a dragon, it could be though of as the journey of our Christian life battling the currents of the world as we press on towards the goal that is heaven.
Now, I know there will be some at the extreme fundamentalist end of the spectrum who will now label us as heretical. Here is a word for you “Just as your (spiritual) ancestors the Pharisees stumbled people from the truth by making it so exclusive, you do the same except with a 'Christian' label. Wake Up! You're stumbling many and saving very few.”