Gin no Guardian

Based on the Chinese web comic Yín Zhī Shǒu Mù Rén.

Sui Gin may be poor, but he is one of the best online video game players. This identity however, is unknown to all except for RikuLei, Sui Gin's classmate. She delivers a mysterious mobile device to Sui Gin but before being able to explain herself, RikuLei is kidnapped and Sui Gin unwittingly finds himself wrapped up in series of problematic circumstances. Searching for a way to save her, he accidentally activates the device allowing him to dive into a new Virtual game-world.

(Source: Anime News Network)