Cole Turnstone is a recruitable character in I Miss the Sunrise.
You will need an EROS access card of at least level 3.
Head to the EROS abandoned databanks and enter the large central room. At the south edge of the room is a computer that lists a number of Surfaces, separated into "Terraform Necessary" and "Terraform Unnecessary". Select "Terraform Unnecessary" and note the coordinates listed under the one marked "CMD: DEL" (0.77.21.08).
Inputting those coordinates will take you to a Surface. Head to the north to find a facility. It requests a password; the answer is Cassidy's code number, 4188. After the cutscene, Cassidy and Cole will join together.
Weapon: Blazing Sky (Auroral/Thermal/Systems)
Requirements: 100 Battle Trust, 10 Typelog fragments collected
Blazing Sky III: 360 damage, 75 Systems cost, 4 AP, Delay
Requirements: 200 Battle Trust, Perfect Auroral Shell
Blazing Sky +:
Requirements: 250 Battle Trust, Ros Rank 20
At 100 Personal Trust: Harden V, Hull Rebuilding III