After some training (ending up at level 53), swapping around some of my S and T type techs, and buying some items in Palamacosta, I head on over to the Thoda Geyser to face Undine, the summon spirit of water, to form a pact so that I can rescue a unicorn.
Undine (26,000 hp) has a surprisingly small arsenal of attacks, only having a dual-horizontal swing with her sword, a faux Aqua Edge type attack, and the Spread spell. However, her raw power more than makes up for it. I opened with a Unison Attack, which finished with Lightning Tiger Blade for super effective damage. Afterwards I rushed her and tried to stop her casting, but with no luck. She is very hard to spell cancel so after a few failed attempts and painful hits from Spread, I either backstepped away or used Tempest to dodge her spells when they were aimed at me. She enters Overlimit about every 4,000 damage, which means her spells are cast a lot faster, so I stayed back and focused on dodging her spells whenever she aimed at me. I avoided her spells and followed up with a full normal hit -> Sword Rain -> Tiger Blade -> Hurricane Thrust -> Raining Tiger Blade combo for some solid damage. I pressed the offensive and kept her guarding so she couldn't start casting again. After her health reach 12,000 or so, she started using the Aqua Edge attack, making approaching her difficult. I used Tempest to get closer and then backed off if she guarded, or finished up my combo if she staggered. After I got her down to 1,400 hp I pulled off one final combo, and finished her off when she was at about 200 hp using Rising Falcon.
So that was the first of the Summon Spirit battles! In the next chapter I plan on facing the Summon Spirit of Wind, Sylph, in the Balacruf Mausoleum!