Delium is a wise professor working at the court of King Yarno IV of Eagle, as he had served Yarno's father and even Yarno's grandfather before. The professor has been studying the use and the history of the fifteen elemental coins for his entire life. He is also one of the few persons who knows about most of their current whereabouts. Of course, Delium would never allow this information to fall into the wrong hands since he knows like no other what the coins are capable of. However, if you manage to save the Eagle Kingdom from a serious threat, Delium will join and share his knowledge with you.
Throughout the course of the game, Delium will often provide you with invaluable advice and insight. In general, this old man is very serious about everything he does and he hates wasting time. It's a widespread fact in the Eagle Kingdom that the professor has actually forgotten how to enjoy himself. In fact, the only times when he actually smiles (let alone laughing!) is when he has discovered something new about the elemental coins. Because of this somewhat cold-hearted appearance, he does not get close with people easily. But he doesn't feel he has to - as long as he can continue his research, he is more than content.
Apart from studying the coins, Professor Delium has also taken an interest in studying monsters. By studying monsters, there are certain enemy skills (also known as "blue magic") that he can learn. This works as follows. First you select his skill "Study". Delium will then check if the monster knows any skills which he can learn, if yes, he will instantly learn it. If he already knows the spell you're trying to teach him, you'll be notified as well. In this manner, you can expand his abilities throughout the entire game. Depending on how much attention you give to this, Delium could very well become one of your most powerful magicians; but if you don't, he will be practically useless. Stat-wise, Delium is very much like the other mages: low HP, low strength, high MP, high intelligence.
In total, there are some twenty blue magic spells, and their effects are most diverse. One of them, the Horny Drop, is acquired in quite a different way. First you have to complete the sidequest to recruit Criss (and Dayanne). After that, go back to the Diamond Veins and confront The Pumba (the boss from Chapter 1). After beating him, you'll see that he had also caught a small guinea pig, named Horny. Catch it and take it with you to the castle. There, it will run straight off to the castle's livestock pen. Examine it with Delium, and you will learn Horny Drop. The good thing about this skill is that you can make it more powerful by feeding the guinea pig pet food - you can do this by talking to Dayanne. Pet food can be bought in Vultura. If you feed him often enough, Horny Drop will easily become one of Delium's most powerful abilities mid-game.
Click the spoiler to see the first half of Delium's blue magic abilities. Take note that he will not get the most powerful ones until later in the game.
-> Learn from Wild Kobolds, Dark Kobolds or Rude Kobolds.
Might - Makes mages stronger by using their mana.
-> Learn from Red Sparrows, Blue Sparrows or Lord Daniel.
Mana Stomp - Destroy an enemy's MP.
-> Learn from Bullies.
Silent Waterfall - A giant waterfall that might inflict silence.
-> Learn from Sirens.
Swarm - Insects deal piercing damage to one enemy.
-> Learn from Mantises, Cutters or Diggers.
Freeze - Shoot ice cubes at one enemy. May stop.
-> Learn from Vault Keepers, Crystal Foxes or Freezopases.
Wheel of Fire - Creates a wheel of fire around an enemy.
-> Learn from Nettles, Minitaurs or Imp.
Rabies Bite - Infect a monster with a berserking virus.
-> Learn from Firefoxes or Fenrirs.
Horny Drop - A guinea pig falls down on one enemy/all enemies.
-> Learn from Horny (see above).
Bio - Damages and poisons all enemies.
-> Learn from Forest Chimeras, Great Chimeras or the Great Drum.