Simon and the Shadoworld.

Simon is Clarry's friend, has been there for him for years, and she drags him into the shadow world, where he is turned into a vampire. Raphaelle the New York clan leader return's him to the institute and she makes the decision to turn him into a vampire, he doesn't like the fact that he is a vampire and clary has dragged him into this world. He would rather be doing the normal things for his age like attending college and playing his music. There is a variation from the books to the show that in the books Simon has a full band, in the show, it is Maurine only. 

He sees that Clary is in danger from the Shadowhunter yet Clary can't explain it but she knows that these are her people and that they can help her make sense of the world that she now is in, as she can see Jace and the others can't as Simon when he is turned into a vampire he doesn't really have anyone to turn to and Alec seems to always be digging him or Clary out of trouble. 

Yet he starts to see his own strengths when they are looking for Clary's mother and later a relic that her mother has hidden from the Clave.  This clip is when they are seeking answers and looking for Clary's mother as she has disappeared and Simon is in the process of becoming a vampire. 

In the beginning, Alec doesn't like Simon as sees him as an extension of Clary, and how that Clary is Valentine's daughter and that this is his world and she has put it at risk, and he is at risk. Because he now rescuing Jace's girlfriend as Jace is his  Parabatai and this means that they are separated from each other when they have made a vow to be together, this vow is like a platonic version of a wedding vow. 

However through the help of Luke and Magnus Simon learns to stand up to people in the Shadoworld, through Magnus particularly as Mangus wants to help the downworlders as he had to figure it out on his own, and nearly killed himself doing it, and therefore he wants to help the downworlders that come into his life but he isn't really patent with them.

 This is Magnus telling Simon to Man up and use his power, as a vampire and the fact that he can walk in the daylight makes him a target, as then he can live a normalized life, he also being Jewish doesn't eat "mundane blood," so drinks animal blood.

 He eventually learns to adapt, to be a Vampire and Down worlder and even starts to stand up to other downworlders the Seely queen, and even the Shadowhunters. Something that the Queen isn't used to and this makes him a target. 

The Seely queen is another complex character that is matched only in complexity by Magnus as she can play the long game as well and sees that the clave hasn't protected the Down worlders as much as they should have so having Simon stand up to her comes as a massive shock to her at times. 

I will do some other posts about how healthy or unhealthy these relationships are in context to reality. Some of these relationships aren't great or healthy at all and create drama. Yet this drama is what makes the show interesting.