Within the Emmy award-winning show Arcane, there is a wide variety of different characters. They all have different motivations and pasts, coming together throughout the show to form a highly traumatized array of factions, friendships, and rivalries. One of the bigger problems with creating a narrative within a massive, highly complex world such that as Piltover and Zaun is that there is only a limited amount of time in which individual stories and character flavorings can be explored.
Something Riot Games and Fortiche Productions do very well is give the audience enough context to understand what is happening and to relate to why characters' motivations are the way they are, but implement the world building technique of half-told stories (setting them apart from many other animated shows). This is the process of giving audiences snippets of characters' lives, and backgrounds, but never truly fleshing them out. This helps not only with cutting down the amount of information needed to be shown on screen, but gives the world of Arcane a ‘lived-in’ feel, a realistic feeling universe akin to our own. One such half-told story that is never properly explained is the history between so-called hero Vander and series master villain Silco, and why Vander tried to kill him.
It’s revealed in the first few episodes that the two opposing characters has a history together, being as close to one another as brothers. They may not be biologically; rather, they're chosen brothers — two people who likely grew up alone on the streets and looked out for one another. The idea of an independent Zaun was one that the two of them shared, likely an idea they came up with to fight back against the oppression and indignity forced upon them from the authorities of Piltover.
When looking at the two characters, it might at first seem clear as to why they parted in such a dramatic way. Silco is a man of indirect violence and destruction, where Vander has adopted predominantly pacifist ways, setting aside his knuckle duster punching weapons (which perfectly sum up his character) and choosing to lead the people of the undercity in a controlled and peaceful manner. He makes deals with the enforcers: peace through diplomacy. Silco, however, is a man willing to fight. He's willing to take that fight directly to the people who oppress the undercity, manipulating others with the use of the highly addictive Shimmer to gain power and control.
However, the flashback scene that shows the polluted water fight between Vander and Silco clouds this idea, as it looks to take place long before Vander's pacifist ways began. The two look young, perhaps even teenagers. Vander persists in his violent ways for a long time after this, shown in the first episode's bridge fight scene. Here, he was leading the charge, fighting bloody to get what he wants just like something Silco would do (albeit through other people). So why did the two fall out years before this?
The answer lies within the two specific problems the undercity faces: oppression and indignity. For Vander, even the violent Vander of the past, his answer to solve the problems of his people was to create the lanes. He created a community of people that would restore the dignity of those oppressed in the undercity oppressed people. He rallied his people to a point where they can live with pride through the love they show one another. Family and stability will lead to independence and dignity.
Silco, however, thinks that the only way to restore dignity to the undercity is through making those who oppose them scared, fearful of both him and the people of Zaun. He does not necessarily believe in the waging of war and the obliteration of Piltover, but he strives to make them fearful of him being able to do so. He stops them sending enforcers down to bully his people, and finally commands respect. He makes himself a powerful enemy to Piltover, and when he is ready, beats them down to the point where they are too scared to fight back. He doesn’t care about how he gets there, flooding the streets with Shimmer to gather power and control. He believes that all the suffering and pain he causes is worth it in the end. With this power comes respect, something Vander himself points out as Silco’s biggest motivation:
‘You had my respect, the lanes respect … but that was never enough for you’
Silco strives for respect, but it’s a more twisted sense of pride that motivates his actions. He's not satisfied with the respect of those around him. Instead, he pushes forward to force others to respect him through fear of what he might do. This describes almost everything he does, as every smooth spoken word that falls from his mouth is laced with subtle threats. He adopts the mantle of the Eye of Zaun, an almost godlike figure to the unfortunates of the undercity. Vander saw the path Silco was on, and realized the only way to stop him destroying everything around him on his quest for respect was to kill him. His failure to do so sending them both down oppositions paths, coming back together dramatically at a point far past rejection for either of them.