There are also a bunch of traditions associated with this day. It seems to be some form of mix of eating a giant norimaki (you know, the seaweed and rice roll that falls into the sushi category although it doesn't need to contain any raw fish) in one go, eating a lot of dried soy beans, dressing up as an ogre, shouting the slogan "out with the demons, in with happiness" while throwing beans around, among the things I know.
So we have a silent understanding; she can celebrate Japanese customs and spend some money on the required accessories without me complaining and I can celebrate such important Swedish traditional events such as Midsummer through the traditional way of dancing around huge phallic symbols and getting dead drunk. Not to mention the August crayfish party which I traditionally celebrate the Swedish way by getting dead drunk (I never really liked those crayfish to begin with so I mostly skip those). I have not yet decided whether I will celebrate the December 13th St. Lucia Day the traditional way of getting dead drunk or not, I might be getting too old for that.