SID bassist AKi will release a mini album, titled "EPHEMERAL", on December 16. It's been revealed that L'Arc-en-Ciel's Ken is participating in the album. 

"EPHEMERAL" will contain 7 songs, and Ken plays the guitar for the last number "The Inside War". You can check out the jacket covers and track list below. 

[Regular Edition]

[Track List]

CD

01. Ray
02. Fahrenheit
03. Sing it Loud
04. In Vain
05. FAIRY DUST
06. Wait for You
07. The Inside War

Limited Edition DVD

??EPHEMERAL?BTS video

Thanks to minlilin for the tip!