Shiva (The After Years boss)

Shiva is a boss in Final Fantasy IV: The After Years. She is encountered in Palom's tale but she cannot be defeated. She is encountered once again in the Gathering Tale in the depths of Lodestone Cavern in the Crystal Chamber. It is necessary to fight her to progress in the story, however if you want Rydia to obtain her as a summon, you will have to be careful not to kill her.

Strategy
Since Shiva has a high amount of HP, it will be hard to defeat her, and even harder if you want her as a summon. If you want her as a summon, you will have to deplete her HP enough for Rydia to state she has stopped attacking. This is difficult, because of her high HP it is a bit difficult to indicate how close you are to killing her. Luckily, you have two Black Mages in your party that know Firaga. Have Rydia and the Man in Black cast Firaga on Shiva, while Edge uses Heal Pill to keep members HP up. Luca really can't do a tremendous amount of damage to her, so just attack Shiva normally with Luca, or if Edge's heal pill isn't enough alone, have Luca use potions on party members with her turn. A good way to tell when Shiva's HP gets close to low enough for Rydia to recruit her, is when Shiva starts using Blizziga every single turn. When she does this, Rydia should stop with the Fire spells, a good move at this point is to use Sylph, if you obtained it before doing this fight. Alternatively, if you have obtained the Recovery Rod, the Man in Black or Rydia can equip and use it to cast Cura on the party. Man in Black should cast a couple of Firas. Continue doing this until Rydia points out that Shiva has stopped attacking. When this happens, do not attack. Just wait, because if you attack Shiva she will counter with Diamond Dust. After waiting for a while, Shiva will talk to Rydia, and Shiva will be yours to summon again. If you don't want Shiva as a summon, (Which is highly recommended that you do get her, because if you don't you miss out on re obtaining Mist Dragon, Asura, Leviathan, and Bahamut.), you can just keep using Firaga on her with Man in Black until she is dead. Note that this will make her use Diamond Dust on you each time as a counter when her hp is low.