Koa Rey is a drug rehab councelor and the brother of current Five-0 member Tani Rey.
Season 8[]
Koa was introduced as Tani's delinquent younger brother. His sister's teammates help procure him a job as a construction worker to better help him keep his life in order. Koa presents himself to work, but continues to use opioids until he suffers an overdose. He is found unconscious by Adam Noshimuri, who rushes him to Noelani.
He survives the overdose and is confronted by his sister. After a tense conversation, he promises Tani that it won't happen again. Tani says his word isn't enough anymore and Koa is persuaded to enter inpatient treatment for his addiction at the Island Hope Rehab Center.
In 8x22, Koa has successfully completed his treatment. He exits the facility and hugs his sister, who is there to pick him up. Tani happily remarks that Koa looks a lot better. However, Koa tells her he isn't leaving: he's been offered a position as a rehab councelor and has already said yes. He apologizes to Tani for making her drive all the way there for nothing, but wanted to see her after such a long time. Koa is later seen leading a support group, where he talks about the importance of love and support in the road to recovery.
Season 9[]
Koa is still working as a councelor at Island Hope. He gives Tani information to help find a missing girl called Alanna. One of the people Tani interrogates in her search for her refers to Koa as "Mr. Rehab", deeming him straight-edged and boring.
Appearances[]
| Season Eight | ||||||||||||
| Fire Will Never Say that It Has Had Enough | Dog Days | Your Knife, My Back. My Gun, Your Head | No Matter How Much One Covers a Steaming Imu, The Smoke Will Rise | At Kama'oma'o, The Land of Activities | Unfolded by the Water are the Faces of the Flowers | The Royal Eyes Rest Above | The Trail Leads To A Diving Place; Do Not Follow After | Death at Sea | The Future is in the Past | A Tall Tree Stands Above the Others | The Round Up | What is Gone is Gone |
| The Children of Kalaihaohia | A Coral Reef Strengthens Out into Land | Only the Stars of Heaven Know Where Pae Is | The Fire Blazed Up, Then Only Ashes Were Left | To Do One's Duty | No One Has Ever Died For the Mistakes He Has Made; Only Because He Didn't Repent | Kind Is the Bird of Kaiona | The Answer to the Riddle is Seen | Though the Fish is Well Salted, the Maggots Crawl | What Parents Will Do, Children Will Do | The Tough Branch That Does Not Break in the Kona Gale | Ancients Exposed | |
| Season Nine | ||||||||||||
| Cocoon | The Man Who Fell from the Sky | When the Sea Draws Out the Tidal Wave, the Rocks Where the Cowries Hide Are Exposed | On the Slope of the Cliff, Not One Jutting Rock is Hidden from Sight | Nothing More the Eyes to Search For | Is Borne on the Back; Is Borne in the Arms | The Smoke Seen in the Dream Now Rises | Birds of a Feather... | Truth Comes from the Night | When the Light Goes Out, the House Is Dark | Gone on the Road from which There Is No Returning | A Bruise Inflicted on an Innocent Person Vanishes Quickly | Those Above are Descending |
| Depressed with the Heat of Kealwalua | Made Prisoner by the Reign of the Rain | When Covetousness is Conceived, Sin is Born | Offer Young Yaro Leaves to | He Who Eats 'Ape is Bound to Have His Mouth Itch | The Octopus of the Deep Spews It's Ink | Way of the Gun | Offspring of an Owl | The Teacher, the Pupil - Let it Come Forth | A Stranger Only for a Day | The Hand is at Fault | Endlessly Pours the Rain of Waianae | |