She's the best, so I'm sad to hear this. I think she easily could have decided to graduate at the end of this year, so I appreciate her decision. Since she is graduating in June, I am assuming her last concert will be their anniversary concert which are held in mid-late June. Assuming international travel is possible next summer, I plan on going.
Also sad that Chika graduated. She was one of my favorites of the next members. I'm glad Yuu came back though.