My name's Lars Doucet, I'm the lead developer for Defender's Quest!
Technically, the game is in public beta for now, so the early release you're playing only has one "magic book" for Azra to equip. We're going to support a good bit more in the final version of the game.
You can definitely access the existing books through save-game hacking, which is the only way to access books other than "furious end" - but beware, anything in the old version of the game might be glitchy or horribly unbalanced. :)
Books will be a big feature in the upcoming expansion to the game, which all of you will receive as a free update. The other big feature is more bonus missions and a New Game+ mode, which raises the level cap and gives you new challenges to play with.
Here's a full list of the ones we're planning (most are already functional in our latest test build):
Chain Lightning - lightning chains to additional targets
Shock Lightning - lightning stuns enemies
Furious Start - newly summoned defenders start frenzied
Furious End - defenders below X HP have frenzy
Slow Start - Newly spawned enemies are slowed
Slow End - Enemies approaching the exit are slowed
Psi Shield - enemies deal PSI damage instead of HP to Azra for the first few hits
Crystal Patch - start with several crystals near the spawn area
Explosive Start - on boost/summon defenders release a small explosion
Explosive End - on defeat defenders release a large explosion
Light of Glory - applies LIGHT to enemies when casting heal
Light of Judgment - applies BLIND to enemies when casting heal
We're still balancing them - some of the more powerful variants will have a small increase to cooldown or casting cost of the associated spell.