Killzone: Characters. That's the best I could come up with.

There are 4 main characters in the story and 3 lesser main ones.. and they all make their contributions.

Playables (main) -- (Jan's Crew)
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Captain Jan Templar - the leader of the pack. He is essentially asked to save the world and along his trip runs into an old friend and they continue on the mission (the friend is Luger who is now playable) Jan is given orders to rescue a spy with Luger and while on their way to the captive's location run across a tank and several soldiers, the two hide realizng their weapons are useless against tanks and all of a sudden some guy starts yelling and shooting at the Helghans. He blows up the tank, and shortly thereafter joins Jan and Luger, Rico is now a playable character. The three go on to rescue the spy who turns out to be the half-human, half-helghast Hakha much to their surprise and displeasure. Jan tries to keep things smooth between Rico and Hakha (he doesn't hate Hakha and knows that this group is going to have to work together if they are to succeed.) When it is revealed that one of the human generals is a traitor, Jan fears for his friend, the general who sent him on his mission as well as a good friend.) Jan decides what his crew is going to do and how, for the most part, and after realizing his friend is dead, heads up into space to stop the traitor.

Shadow Marshal Luger - a cold and calculating female assassin / spy. It is revealed that Jan and her once had a semi-romantic relationship, but that ended awhile ago when she went for her training and lost many of the more human emotions. Rico notices tension between Luger and Jan, and Hakha explains what most likely happened - she was "trained to act, not feel." There does not seem to be much chance of rekindling a relationship between her and Janm but they do work well together on the battlefield.

Sergeant Rico Velasquez - the big "tough" one, he carries a large chain gun capable of destroying tanks.. He hates the Helghast more than anyone (on the crew at least). For this reason, he dislikes and distrusts Hakha, often threatening to kill or maim him, and the two constantly exchange insults throughout the game. However, as the game continues, the hatred/distrust between the two fades a little, but not entirely- they are both valuable and essential components in the team, it is only 4 people after all.


Colonel Hakha - Half human and half Helghast and a spy; for these reasons, but mainly the first, the rest of the team does not entirely trust or like him, especially Rico. Over the course of the game he proves his loyalty, from shooting a Helghast soldier when the other 3 playables find him, to figureing out who the traitor in the Human military is, and eventually killing a major Helghan general after he (the general) reveals that he personally killedHakha's brother for his pro-human ideals.


Non-playables
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General Bradley Vaughton - A human and friend of Jan Templar. Vaughton orders Templar and Luger to find and rescue an important person(who turns out to be Hakha.) He is betrayed by General Adams and then executed.

General Stuart Adams - Another human general, he turns out to be a traitor and hands the human's space-based weapons platform over to Helghast control and gives the order to execute General Vaughton. This of course causes some tension and overall hatred between Jan and his crew, but especially Jan.
At the end of the game, whichever of the characters you are playing will be the one to have a part in his death(although, the player doesn't kill Adams, falling debris does.)

General Joseph Lente - A general and Commander-in-chief of the Helghan army under direct command of the Helghast leader. He loathes humans and Earth and leads many of the major assaults on Vetka. After he is defeated by Jan's crew, he reveals to them (mostly Hakha) how he killed Hakha's brother. When Hakha puts a bullet in his head, his loyalties seem pretty clear to the others.

Shapes
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There is no character triangle for romantic relationships, just a line that is faded between Jan and Luger. As there are 4 main characters, there would be mostly character squares.

One triangle would/could be Hakha-Hakha's brother(we never see)-Lente.
Hakha is a half-human half-Helghast individual, so he could belong to either side.
His brother was a pro-human idealist.
Lente, a Helghan with major human-hating qualities personally kills Hakha's brother.
Hakha now (even more so) hates Lente and the Helghast, sides with the humans, and eventually kills his brother's killer.

Jan-Vaughton-Adams
Jan and General Vaughton were friends
General Vaughton and General Adams were friends
General Adams betrays the humans and has Vaugthon murdered
Jan does not like General Adams, and goes on a mission to stop / kill the traitor.

Some of the major character developments included Hakha proving his loyalty and value to the pure humans as the game went on and Rico's hatred for Hakha lessening as Hakha proved himself, and Hakha's dislike of Rico lessening as Rico's dislike for him lessened.
The relationship between Jan and Luger is revealed a bit more as the story moves foward, as is how/why it eneded and how the two changed since then (particularly Luger).

Each of the playable characters has their own distinct weapon(s).
Jan uses a standard ISA machine gun
Luger uses a silent semi-automatic-ish semi-sniper rifle.. it is very quiet, has a good scope, shoots single rounds or can shoot several (becoming louder). She also wields a knife.
Rico uses a chain gun that holds something like 8,000 bullets as well as rockets. It is loud and big and can overheat after too much use (stopping the player from just shooting all 8,000 bullets in a minute)
Hahka uses the standard Helghast machine gun, its a little slower than Jan's gun but hits harder and holds more bullets. Like Luger, he also has a knife, though his looks more Helghany.