'Negary' already knew about the existence of a powerful spirit inside the institute, coupled with the fact that Roger's group never really concealed their movements in the past made it very easy for 'Negary' to generally infer the spirit's identity.
Not too long ago, 'Negary' found a book called [Theory of Spirit Summoning Rituals] from the Mobis Institute's library, which depicted in detail the method to draw out one's own spirit.
Thanks to Roger, 'Negary' was able to find the sealed classroom as well as the events of 10 years ago.
There used to be a student called Field who was most likely exactly the same as Roger, gifted with a naturally potent spirit sense, capable of seeing many things that others couldn't. He seemed to have entered the Grand Library and obtained the [Theory of Spirit Summoning Rituals] from it.