Castling

Castling is a Summoner skill in the MMORPG Elder Tale.

Description
An emergency escape spell that allows the Summoner to immediately swap positions with a Summon Servant. Because Castling only requires a blink of the eye to activate, it is possible to use it to evade attacks right before they reach the Summoner.

However, Summoners who use this skill in an absolute crisis must be prepared to sacrifice the Servant. It is useful in a combination with Soul Possession, usually used to get past terrains that are difficult to traverse as a human.

Go East arc
KR collected information about overseas servers after the Catastrophe by using Soul Possession. He managed to meet up with Kanami and her party in China, although she only used him as a riding mount.

After Kanami, Coppelia, and Elias Hackblade go on to challenge the Genius without Leonardo, KR uses Castling to bring himself from Yamato to China and participate in the battle.

Route 43 arc
Roe2 told the kids she used Castling to switch places with her brother to get to Oou from "far away" (i.e. the moon).