This is Sisi, the Zither Nympha from Girls Symphony.

The zither is a stringed instrument from the Alpine region.

I believe Sisi's name comes from the nickname of Empress Elisabeth of Austria, who was a zither player.

It seems there are various spellings, such as "Sisi," "Sissi," and "Sissy."

Here, sisi is holding the zither while playing, but in reality, it is generally played resting on a table.