Catch up with the first installment looking at "Kuroko Shirai"
Catch up with the second installment looking at "Accelerator"
Catch up with the third installment looking at "Takitsubo Rikou"
Esper power: Meltdowner
Shizuri is a member of ITEM, a mercenary group in the dark side of Academy City that Misaka encounters in Railgun S. Being the fourth ranked Level-5, Shizuri is the most powerful member of ITEM and the closest opponent after Accelerator to give Misaka a real run for her money.
You might've also seen Misaka redirecting Meltdowner in some of the clips I've shown. Well that is a two-way street. Since Meltdowner functions a lot like Railgun, Misaka can bend Mugino's Meltdowner away from her. Consider the fact that Mugino is also a Level-5 Esper just like Misaka. The only difference is, unlike Misaka, ITEM works together as a team which makes taking them down nigh-impossible.