She's either moving or repairing Earth by becoming the Earth's core.It's the only things I can think of that she'd do,since she wants to protect the world,and those she loves.Becoming the Earth's new core would most likely repair Earth.Ultimately,this chapter made me sad.Aya deserves to not be miserable,and live out her life being happy with her twin sister,Yatsumura(no yuri intended,just siblings separated at birth finally being able to be family again.),it's all I really ask for,but I expected a sad ending once I jumped on this ride.