"Gunjō Biyori" , also known by its English name "Ideal Days for Ultramarine", is the debut single by Japanese rock band Tokyo Jihen, led by musician Ringo Sheena. It was released on September 8, 2004, ten months after Sheena's solo single "Ringo no Uta".

Yumiko Shiina , known by her stage name Ringo Sheena , is a Japanese singer, songwriter and musician. She is also the founder and lead vocalist of the band Tokyo Jihen.