Selfish Fairy Mirumo de Pon! Wonderful

One day, Kaede and Milmo met a strange creature. It was not a human or a fairly, but it was Tacos, an octopus-type robot. He said, I'm looking for the seven crystals dispersed in human and fairly worlds. I've been looking for them all over the world, and I finally found they were around here. But I got tired... Will you help me search for them? This is between us, but if you collect all the seven crystals, they will grant you any wish. Because it was too absurd, they wouldn't listen to him. But he was eagerly to ask them, and Kaede and Milmo decided to look for the crystals for him. Tacos turned her fairly call into a fairly call crystal in return. Fairly call crystal has a function to detect a crystal, and it can cast a session magic by combining their forces. What is the real purpose of Tacos? What is the true role of the crystal?