After the battle inside the Ziggurat, Chizuru and Hayate are horrified to find out that their victory would have cost Koyori her life. They agree to help Tazuna and Koyori, even though they're out of the fight now.  They tell the two of them that in order not to be found in the real world, they need to come up with a name to use inside the Ziggurat when they fight.  After a bit of thought, Tazuna and Koyori's new name becomes "Single Gear".
I have theories, but haven't 
been able to prove them yet.
لديّ نظريّات، لكن لم أتمكّن من إثبات
أي واحدة منها بعد
Ich habe da eine Theorie,
aber noch keine Beweise.
Tengo una teoría,
pero aún no puedo verificarla.
Tengo una teoría,
pero aún no puedo verificarla.
J’ai plusieurs théories,
mais aucune preuve concrète.
Ho un'ipotesi...
Tenho algumas teorias, mas não
 consegui provar nenhuma ainda.