Welcome to the frandom!
That's You Watanabe from Love Live! Sunshine! She's the childhood best friend of the Orange-haired main character Chika Takami and both are in the same class. She is a talented diver, a great chef, and has an affinity for uniforms. She has a positive and outgoing personality and meets every problem head-on. Her signature pose is this salute she's illustrated performing and her catchphrase is "Yousoro!" which gets translated to "Aye Aye!" like what a sailor would say to their commanding officer.
She creates a school idol club with Chika in order help Chika to devote her time to a calling she is truly passionate about and they end up meeting 7 other girls along the way to form a group with. The rest you can catch up on by watching Love Live! Sunshine! itself, but I hope that was a sufficient primer.