This special Redmi Note 4X will hit the market on February 14, right on this year's Valentine's day. Its bundle includes a Hatsune Miku branded back case, as well as a Mi power bank.
http://www.notebookcheck.net/Xiaomi-unveils-Redmi-Note-4X-Hatsune-Miku-limited-edition-smartphone.196396.0.html