You are bound.
Eris has successfully bound your Light to that of Crow and Zavala, enabling you to traverse the Leviathan with some measure of protection from the Nightmares there.
"Calus has begun to forge a bond between the Leviathan and the dormant Pyramid buried on the Moon," she says. "I do not yet know why, or how."
You are tasked with exploring the Leviathan to uncover the truth behind Calus's mission, and gather essential components so that Eris can begin severing his connection to the lunar Pyramid, which will mean confronting one of the ship's most powerful Nightmares.
"You will assist Crow when it comes time to perform the first severance ritual. We both know what form his Nightmare will take," Eris warns you.
There is no turning back now.