There is very little dialogue in this game, and what there is of it is presented in a strange language (with subtitles), so you are often forced to throw in your own interpretations of what exactly is going on. You arrive on horseback at an ancient temple with an unconscious (dead?) young woman in your arms. You lay her down on a pedestal, and suddenly an etherial voice charges you with killing some of the ancient colossi that roam the world. Your sword, when held aloft, will shoot a beam of light that narrows when you shine it in the general area where a colossus resides, and that's about all you get. Fun times.
Finding a gargantuan colossus is not always easy, but once you manage to track one down, you begin to realize the enormity of your task. Colossi are only weak on a certain area of their body covered with a glowing rune, and they don't necessarily want to present that rune to you. To reach these runes (often on the very top of their heads), you have to physically scale the beast, grabbing on to fur and horn outcroppings to give you a small handhold while the colossus roars and attempts to shake you off and attack you. In addition to your climbing troubles, there's not really a straight path to the rune, and oftentimes you are required to puzzle your way from ledge to fur to ledge, searching for the rune. Once you find it, you grab on with one hand and attack with your other, and if your grip doesn't fail (you have a limited reserve of strength), and the rune doesn't move, you'll eventually bring the creature down.
This part of the game is where, at least to me, it gets morally ambiguous. Some of these colossi attack you on sight, and all you can do to defend yourself is to kill them and take them out of the picture. However, some are completely docile, and remind you of simple beasts, just roaming their land in peace. Aggressive or not, you still have to attack and kill all colossi you find, and this casts an interesting light on the nature of your quest.