The Mysteria

The Mysteria are four questions with four answers held by four different houses that are part of the Guild, or once were. The four houses are Eraclea, Bassianus, Hamilton, and Dagobear.

Mysteria is plural for Mysterian (which is obviously singular)

When a mysterian or the mysteria or spoken, ships, instruments, weather, etc. begin to act oddly. In episode 11, "Develop" Dio speaks his houses mysterian to Alvis. This causes Alvis to glow, the weather turns for the worst, and the Silvana's instruments began going haywire.

We also know that each house knows the question portion of the Mysteria as it seems that is the only thing Alex was able to get ahold of throughout the series. When the questions (or first part of a mysterian) were spoken infront of Alvis, she would know the answer (or response) to the first half.

For an unknown reason, Alvis is the only person who is able to give the second half of each mysterian, and the only one able to actually awaken Exile.

In the last episode, after each mysterian, Exile reacts in some way. Either by lowering it's cocoon, or clearing the sky of the grand stream (which happens after three mysterian are spoken)