When Capcom announced Karin would join the cast of Street Fighter 5, it was a joyous occasion for most old school fans of the series. While some people keeping an eye on the Tokyo Game Show announcement may have thought Karin was a new character (shame on you!), she's actually from Street Fighter Alpha 3.
Karin's look hasn't changed all that much. She seems a bit older, but otherwise this is essentially the same design she rocked in Alpha 3. However, her moves have changed to better fit in with the Street Fighter 5 game mechanics. Many of her animations are similar, but the properties on the attacks were adjusted.
Let's begin with Karin's command normal, the Tsumujigari overhead. This is a fairly standard overhead attack, but it seems to cover a decent amount of range. However, it's not Karin's only overhead attack. Her Ressenha (Quarter Circle Back+Punch) is also an overhead attack that travels even farther depending on the strength of the punch button used. You can follow this with down and Kick or up and Kick to get a low sweep or a throw, respectively. The EX version of the Ressenha is essentially Karin's Dragon Punch.
Karin also has a command dash in the form of the Kanzuki-Ryu Hokojutsu Sappo (Quarter Circle Forward+Kick). If you played Street Fighter 4, you can think of the command dash like you would Ibuki's, but this one seems like it could be a bit more useful. It covers about twice the distance of Karin's normal dash, and you can cancel a normal into the dash.
There are also two attacks you can perform off the dash. The first is a launcher by pressing any punch button, and the second is a shoulder tackle that leaves the opponent standing. The EX version will stagger the opponent so you can perform a follow-up attack.
Rounding out Karin's special moves is the Mujinkyaku (Quarter Circle Back+K). This is a double kick attack that changes based on strength of the kick used. This is essentially combo filler as you don't get much after any of these attacks connect.
Karin's V-Trigger and V-Skill is where she truly shines. Her V-Skill is the Meioken, which can be charged by holding down the buttons, and absorbs projectiles if you connect with the tip of Karin's palm. If the V-Skill is blocked or connects, Karin builds her V-Gauge.
Once the V-Gauge is full, Karin can unleash her V-Trigger, which is the Kanzuki-Ryu Guren no Kata rekka or Guren Series for short. Karin has a variety of options off of her Guren Series, including the ability to perform a cross-up, go low, overhead or use a command throw. She is very scary once V-Trigger is active, especially in a skilled player's hands.
Karin's Critical Art is the Kanzuki-Ryu Hadorokushiki Hasha no Kata. This is fairly easy to combo into as you can hit-confirm off a Guren Series or even juggle with it after Karin's command dash launcher. The damage isn't quite as high as some of the other Critical Art attacks in the game, but with the right hit-confirm combo it can be fairly devastating.
With Karin's only decent reversal coming from her EX command dash, the super meter is important to her. Unless you can get a hefty lead to finish a match with a combo into super, it may be best to save Karin's meter for her EX special moves. You'll have to judge each situation carefully instead of just going for the super every time it becomes available.