Took me a while to catch up, since I was watching Lunar's instead of Ureshii. I really love this series though. It reminds me a lot of Darwinia, if anyone has ever played that. The mysteries are really piling up already. The key that 'evil' Yuko has, the lock around Densuke's neck, whatever Yusako's 4-4-2-3 code and her keyhole means...
The best part of the series so far is the creepy grandma. Her face when she's shooting the Megane Beam and the mojos is priceless.