The Commander and The Chief (Mass Effect x Halo)

John Sheppard, an N7 Alliance Marine and one of the Spectres of the Citadel Council, has a mission of taking down the rogue spectre known, Saren Arterious. However, another mission is given to him by Admiral Hackett, a mission about a distress signal from the dwarf planet Pluto. Not knowing anything about it. Nobody knew that a hidden Cerberus lab is also hidden there, just close to Earth.

Sheperd will be, Spacer/War Hero/Soldier

PS: I played Mass Effect 1-3 a lot of times until this idea pop in my brain :3