It made sense that no one other than the twins' group noticed Vuccu. After all, Rean always kept his Divine Sense Bending Skill active, albeit only slightly. That way, he wouldn't really bend any Divine Senses, but would still feel any Divine Sense touching it.
As for how Vuccu's Divine Sense was getting inside the Formations from Qufis, that was quite simple. The formations were made to stop at most Divinity Realm Senses. Who would expect a Celestial Realm expert to come into the Future Realm? Qufis could build one capable of such a thing fairly easily, but that would have taken time and resources, which didn't make sense to spend.
