I guess those in Tokyo would already have ticket but figured I might try anyway. I have an extra ticket for this event the 23rd of February. It's number 63. It's 2,500 yen.
According to the website, you will be able to take a polaroid picture together with Riyu. She will also perform some songs, and sell her new album and photobook. Also something about a movie called Axion, and she will give out some signs and presents. Not sure.
小坂りゆのメッセージ ブログ:◇◆◇２月２３日（土）小坂りゆ イベントチケット販売のお知らせ！◆◇◆ - livedoor Blog（ブログ）