I know that there is also an Arc The Lad anime, but I have no idea whether the anime was based off of this game, or whether the game was based off the anime (I'm going to assume the latter, rather than the former). Either way, this is my first experience with this series.
The game is a tactical RPG for the Playstation® 2. Surprisingly, it's actually very good. I'll talk a bit about the game mechanics.
The combat system works much like Final Fantasy Tactics, only without the grid. When it's one of your characters' turns, they can move freely within their movement range, and then attack, use special abilities/magic, or pick up/use items. Unfortunately, once you take an action, your cannot move afterwards, even if you did not move at all beforehand. Fortunately, they took a page out of FFT's book, instead of Disgaea's book, when handling XP rewards. You get XP for performing actions, instead of just for slaying an enemy. You also get SP, which is used to learn special abilities and magic, and to raise your Class (which makes more special moves/magic available for you to learn).
Upgrading weapons and armor is done through applying Weapon Parts or Accessories to your weapon or armor. Every character only ever uses one weapon and one piece of armor. In this world, people are attached a bit more to their equipment, and look for ways to improve upon what they already have, instead of just buying new stuff. You can basically equip 3 Weapon Parts and 3 Accessories at any given time, and their effects range from just higher attack and defense boosts, to adding elemental damage, or allowing you to hold more Spirit Stones. In this manner, your equipment is entirely customizable.
Special Abilities and Magic (henceforth referred to as "Skills") are governed by a sort of unique 'MP' system. All characters have a maximum reserve of "Spirit Stones." Spirit Stones are required to use Skills as if they were Magic Points in any other RPG. The catch is, you can't restore them just by resting in an inn like in other RPGs. A Spirit Stone, once used, is gone. So to replenish your effective MP, you have to either find or buy replacement spirit stones. They really aren't very rare, though. They cost 2G each in Item Shops, and drop frequently off monsters. If you constantly use Skills, though, you may find yourself running low.
Inventory is handled by making used of both a Party Inventory, and an individual character Inventory. Items in a character's inventory are available for that character to use in battle. You can move items between inventories freely outside of battle, or just before battle begins. Which reminds me, before each battle begins, you are given a screen to choose the participating characters, and also manipulate your inventory, skills, and other aspects, allowing you full preparation before heading into battle. Quite handy.
Gaining monetary rewards, and other loot is handled during battle. When an enemy dies, it may drop one of three things: An item, money, or Spirit Stones. These are represented by white, gold, and blue sparkles on the ground, respectively. You must move a character to them to pick them up, otherwise you will not get anything at the end of the battle. This isn't much trouble, though, as you can usually attack an enemy from the place where you picked up another enemy's dropped items. Enemies don't seem to want to take these things from you like they would take chests or crystals in FFT. Unfortunately, you don't get rewards just for finishing the battle, like in FFT. Fortunately, the game's economy is adjusted to reflect the fact that you don't gain thousands of G for each battle you win.
Also, there is a combonation attack system built into the combat. After a certain amount of fighting, your characters will be surrounded with a fiery aura. At this time, if you initiate an attack on an enemy while there is another character within striking range to that enemy, they will attack together with a powerful combo attack.
Another plus for this game, is that it doesn't seem like you really have to do much "grinding" outside of storyline battles.
And now a few things about the look and feel of the game.
The graphics are actually highly detailed and quite beautiful, especially for an older PS2 game (2003). The characters have unique designs, environments have distinct personalities. The characters have feelings, and you can get emotionally attached to them. The voice-overs, while unfortunately sparse, are done rather well. The story is ingrossing and addictive. Sometimes there will be long forays into the storyline without seeing a battle, but that's okay. When outside of battle, you don't just go to different points on a map looking for a new battle, you can explore towns, and visit different areas. Navigating the world map is done by waypoints, however.
The story is actually split between two main characters. One is Kharg, the son of the former Queen of his country (who abolished the monarchy and turned the country into a free country) with desires to be strong and protect his country from the evil Deimos (very intelligent monsters). The other is Darc, a Half-Deimos who is the slave to a fat ugly hag, and must deal with being an outcast in Deimos society, along with somehow trying to fulfill his father's dying wish - to save the Deimos who despise him.
For anyone looking for a decent RPG, and likes a bit of a tactical aspect to their combat, then Arc The Lad: Twilight of the Spirits is probably for you. I certainly reccommend it. And used at Gamestop for $15 isn't bad at all.
I give it a 4/5.
I own the set of it.
I'm not sure if the anime was first or not, though. I want to say the game was.
Lyinar Ka`Bael, Piney Fresh Druidess - Luclin
The characters are actually highly uninteresting and generic (except for Darc's buddies, who are kind of cool) and the gameplay is so-so. You might enjoy it simply because there are almost no tactical RPGs anymore.
A 'C' game at best.