Tales of Symphonia has an amazingly complex and twisted storyline. It would be impossible to share every nuance here (although, if you have a detailed summary we'd love to post it ^_^ Full credit to you of course.) Since it's been a few months since we've played this will be a very generalized view and probably a little jumbled... but here goes.
"Once upon a time there existed a giant tree that was the source of all mana. A war, however, caused this tree to wither away, and a hero's life was sacrificed in order to take its place. Grieving over the loss, the goddess disappeared unto the heavens. The goddess left the angels with the edict: "You must wake me, for if I should sleep, the world shall be destroyed." The angels bore the Chosen One, who headed towards the tower that reached up unto the heavens. And that marked the beginning of the regeneration of the world."
~ The game intro ~
"Two worlds exist, unaware of each other. Mana, or life force, is shared by both worlds and while one world thrives, the other suffers.
Lloyd Irving lives on Sylvarant, a dying world where nothing is as it seems - a fact he hasn't yet realized. With a strong set of justice, incredible bravery, and a particular loyalty to his friends, he joins them in a very important quest: a journey to save their world.
Lloyd's close friend, Colette Brunel, is the Chosen One, destined to save the dying world as a descendant of the Mana bloodline. At the age of 16, the weight of the world hangs on her shoulders.
Genis Sage, the village intellectual, is a talented magician with a personality to die - or kill - for. Most likely, you'll grow to love him.
Together, they set on this dangerous journey together - to unlock the seals of the world and bring the balance back to their dying town on Sylvarant."
~Official Namco Tales of Symphonia site~
Lloyd Irving is an orphan, adopted by a dwarf. His best friends are an elf named Genis (who is young but brilliant) and a girl about his own age named Colette. Colette is kind and sweet and loyal... and she's the chosen one. The story opens with us (being Lloyd) asleep in school... seems he isn't the greatest student. A history lesson is interrupted by a bright light from the temple. The teacher, Professor Raine Sage, runs to check on it (believing the time for the chosen has come), leaving the children to their studies. But Lloyd isn't one to sit still while something is happening, and Colette and Genis can't let him go alone, so the three friends head to the temple.
They find it under attack but what appear to be Desians, a race of half elves that currently oppresses the rest of the people of Sylvarant. They are a little surprised by this attack since their town, Iselia, has a non-aggression treaty with the Desians. The Desians evidently want to kill Colette. Lloyd and Genis put up a brave fight, but it is a wandering mercenary, Kratos, who saves them. Kratos offers to help Colette get through the temple (a necessity as she is the Chosen and this is the day of prophecy), but she won't go without Lloyd. Together they enter and find Remiel, an angel who they believe is Colette's true father. He begins Colette's transformation into an angel and send them toward the next temple - near the desert city of Triet.
It is decided that Colette will set off the next day. Kratos is hired as her bodyguard, and Raine will accompany them because of her knowledge of the prophecies. Lloyd wants to go but is told that he cannot. Upset, he heads home. Genis asks to follow him, saying he wants to visits someone. The someone turns out to be Marbel, an old woman being held at the local human ranch. A few important points: A human ranch is a facility where the Desians enslave humans for the purpose of cultivating exshperes - strange stones that enhance fighting ability, stamina, and many other physical stats; part of the Iselia non-aggression treaty is that they will not go near the ranch for any reason. Considering all this, Lloyd can't let Genis go alone (Genis is only 12) and so he accompanies him.