The First Year Arc is a story arc in the Toaru Kagaku no Railgun manga series, covering chapters 131 onwards.
Tokiwadai Middle School
At the start of the school year, Tokiwadai Middle School was dominated by three main cliques, referred to as Tokiwadai's 'big three' cliques; in order from largest to smallest and first to last, they were the Sha Clique, the Mikagami Clique and the Hasekura Clique.
The largest clique was led by second year student Sha Danshan, said to be the closest to the title of "Majesty" at the time. Sha and her clique believed that the gifted had a duty to do volunteer work (such as buying and greening deserts) and its members were dedicated to service, earning them popularity and power. It was suggested that their efforts might have been to thank for Tokiwadai being considered one of the top five schools. It was also suggested that the secret to Sha's popularity might have been the protective desire inspired by her weakness and frailty, having a weak constitution and being nicknamed the Infirmary Empress.
The clique in second place was led by third year student Mikagami Nagisa and of the three, was said to be working the hardest to get results. The Mikagami Clique was apparently made up of students who were mostly drawn to her oil control ability and sought her to fulfill their own desires (such as manipulating fat in their body to enhance their bust or slim them down), with Mikagami only doing this for those who contributed the most to her clique. The clique in third place was led by third year student Hasekura Reiri, the oldest but overtaken by the other two (supposedly without intending to). It was described by one of its members as a carnivorous clique, with members willing to throw others under the bus to succeed.
One student whom Misaka Mikoto would encounter and interact with was Shin'enkouji Rurikakesu (Ruri for short), a second-year student noted to be a free spirit who refused to fit the mold and whom not even the teachers could control, and someone whom the three main cliques had an eye on. Another one was Kessai Kiyoshi, a first-year student who was her first roommate and a member of the Hasekura Clique, for whom she was monitoring Mikoto.
At the start of the new school year in April, two Level 5 espers entered Tokiwadai amongst the incoming first year students, Misaka Mikoto and Shokuhou Misaki, realizing the school's dream of having a Level 5, but also having some effects among some of the students. Among the big cliques, there was apparently a wish to avoid their competitors taking in a Level 5 but also a concern that the Level 5 would take attention away from the clique leader and disrupt the status quo within the clique if they took them in.
Shokuhou Misaki entered the school from Clone Dolly as part of a deal she made with the Board member with authority over Tokiwadai to suspend support to Shundou Toshizou and Ideal. Shortly after the deal was made, the Board of Directors approved her promotion to Level 5. At the time, she was small and lacked the figure she had one year later, being described by people as looking like a doll.