"Well, a Summon Spirit is also known as an Elemental Spirit. They control the mana of the different elements--like Fire, Ice, Water and so on. If they make a pact with you, you can Summon them for help." Hence the other name.

"I've made pacts with those of my world, and they're here with me." Now the hesitation kicks in. "Aaaand sometimes I spar with them. Sometimes things get out of hand." She lifts her bandaged hand for emphasis.

"I was sparring with the Spirit of Lightning, Volt." Despite her calm tone, Sheena puts enough meaning behind those words that it's clear to anyone that this is something more than just a sparring match gone wrong.