What was Mithos's vow(s) to the Summon Spirits?

Question

during the events of Tales of Symphonia where Sheena is making the pacts with the Summon Spirits they all talk about already having a vow with the Hero, Mithos (with the exception to Volt)

I am up to breaking out of Welgaia and have learned that Mithos is

Lord Yggdrasil, who's real name is Mithos Yggdrasil

now given the above and how Sylvarant and Tethe'alla work i could assume that Mithos's vow is something along the lines of

keeping the world split in 2 and/or to protect Martel from the Great Seed

however when Sheena went to make a pact with Volt, Volt said that Mithos broke his vow and this lead Volt to lose faith in people and not want to make a pact again.

Now Sheen's vow has changed over the course of the game so they don't all have to have the same vow, however all the spirits but Volt have not nullified their pact with Mithos so one would suspect that their vow is vastly different to Volt's

So what was Mithos's vow(s) to the Summon Spirits? particularly the one with Volt which was broken

Answer 1

It was a promise that he would restore the Great Seed to the world so that it could grow again, thereby restoring mana to the land. Instead, Mithos took it to Derris-Kharlan in order to revive and protect his dead sister, thereby breaking his pact with the Summon Spirits.

The pact that Mithos made with Volt was not one of a promise, Mithos's pact with Volt was to use his power. Because of how Mithos acted after gaining the use of Volt's power via the pact formed, Volt became angry at the misuse of his power. This is similar to how Lloyd's group uses Volt's power to energize the Rheairds.

The other Summon Spirits are able to communicate with Mithos with forming the pact, and didn't accept a "use my power to do whatever you want" pact - he had to be more specific. The only reason Lloyd's party was able to communicate with Volt was the addition of Raine.

Since Mithos technically didn't do anything but use Volt, he didn't break a vow.