Double Seven Series 2 was published in Dengeki Bunko MAGAZINE Volume 29.
Double Seven Series refers to the short story segments written by Sato Tsutomu released in Dengeki Bunko MAGAZINE in a timeline when Shiba Tatsuya and Shiba Miyuki enter their second year at First High.
It is now published in light novel format as Volume 12, chapter's 5 and 6.