Unnamed Memory, Vol. 6 (light novel) — Kuji Furumiya

The Eleterria, powerful twin orbs with the power to change the past. Oscar and Tinasha have one, but the other has vanished. Even alone, the mysterious artifact can change the course of history, and there are many who will stop at nothing to obtain it. With danger erupting from all around as their wedding approaches, will the king and witch be able to protect the orb from falling into the wrong hands? The pair's nameless story of love and adventure comes to a climactic end!