Back when I was at university, I tackled the subject of emotional attachment for my final-year dissertation. I asked the question: what makes players form a bond with the characters that inhabit the worlds of their games? In order to answer this, I first needed to determine which characters (NPCs, specifically) were successful at doing this in the first place.
I threw the question to gaming communities across the web (including this one, in fact), and two names dominated the results: Ico's Yorda and Shadow's Agro. I'll avoid the specifics of the study, but - skirting around the actual crux of my thesis - you could boil the results down and say that Ico and Shadow of the Colossus are the two most emotionally engaging games of all time.
Ten years down the line, with HD revisions of both titles on a single disc, this still holds true. Those that have played the pair before will know the characters well: Yorda is the helpless girl you take by the hand and lead through a bleak castle, and Agro is the trusty steed who ferries you about the misty peninsula inhabited by towering golems known collectively as the Colossi. Part of their success, I argued, is that they're intrinsic to the core mechanics of the game. But it’s more than this: Yorda and Agro succeed because of the context and setting surrounding them. This is what defines each experience, and is the reason they're widely regarded as two of the best games ever made.
Fumito Ueda and Team Ico are masters of pulling the player into the worlds they've created. The tactics employed in doing this are simple: get rid of every non-diegetic device that reminds you that you're playing a game at all. There are subtitles for the rare snippets of conversation, but everything else you'd normally expect from has been banished. There's no health bar, no resource meters, no score - no HUD at all, in fact - no collectibles that disappear when you run over them, and no loading screens. It's just you and the world behind the screen.
Ico, first released in 2001, tells the story of a young boy who is banished from his village due to the horns sprouting from his head. He's strapped to a horse by the leaders of his village, taken to an old castle tucked away in a sprawling forest, incarcerated in a small egg-shaped prison, and left for dead. After rocking the little prison off its shelf, Ico manages to break free, and so his adventure begins. It's not long before he meets a pale young lady by the name of Yorda; a fragile little thing that is unable to speak the same language as our horned protagonist, unable to defend herself from the shadowy creatures that pursue her, and totally incapable of doing anything by herself.
And therein lays the mechanic at the heart of the whole experience: getting Yorda safely from A to B, helping her to escape the prison that is her castle. This involves grabbing her by the hand with the R1 button (a tactic employed recently by Molyneux in Fable III), and ensuring she comes to no harm as you work your way out of the citadel. Whilst there's a reasonable amount of platforming involved in doing this - leaping across chasms and shimmying along ledges - it relies mostly on puzzles; working out how to traverse an environment and ensuring Yorda - who can't jump or swing from chains like Ico can - gets there safely, too.
This was the first example of a device we've since seen in Enslaved and Majin and the Forsaken Kingdom, amongst others, an experience now known as 'partnership gaming'. Unlike the key NPCs in these games, however, Yorda has no abilities of her own. She can't even cross a room without being yanked from one side to the other. She's entirely dependant on you, and this is precisely why you end up caring for her so much. You'll take great pride in swinging that makeshift sword, fending off the foul creatures that are trying to prevent her escaping. There's no special moves or combos to help you do this, you simply press a button to swing your sword, and if it hits the buggers enough times, they'll die.