Wally West, aka Kid Flash, (Keiynan Lonsdale) returns in The Flash season 6 but where has he been since season 4? The Arrowverse series centering on Barry Allen (Grant Gustin), aka the Flash, has spawned a whole family of super speedsters, both good and evil, but Wally West traditionally ranks second only to Barry himself in the Speed Force hierarchy. Yet Wally has been absent from The Flash and the Arrowverse in general for quite a while and here's why.
Wally, the son of Joe West (Jesse L. Martin) and the brother of Iris West-Allen (Candice Patton), debuted in The Flash season 2. He gained superspeed powers in The Flash season 3 and adopted the moniker of Kid Flash, running side-by-side with Barry Allen in several adventures as a key member of Team Flash. (Interestingly, in the Flashpoint timeline, it's Wally who becomes the Flash.) The younger West also had a love affair with Jesse Wells aka Jesse Quick (Violett Beane), the Flash of Earth-2 but when she broke up with him, Wally found himself feeling aimless. Though Wally left The Flash in season 4 to find inner peace, he didn't exactly disappear. In fact, Kid Flash played significant roles in several major events before taking a prolonged leave of absence from the Arrowverse.
After Wally left Team Flash in season 4, he spent some time in Blue Valley where he found time for both "self-reflection and a battle with a starfish from outer space". Wally returned to Central City for his sister Iris' wedding to Barry and to help the superheroes fight off an invasion of Nazis in the Crisis on Earth-X crossover. During the Nazi invasion, Wally whisked Joe and his fiancee Cecile Horton (Danielle Nicolet) away from Central City to keep them safe. Weeks later, Wally was unable to attend his father's Christmas party because he was traveling in Cambodia. While Team Flash battled Clifford DeVoe aka The Thinker, Wally remained in Asia and continued his journey of self-discovery, growing more centered and zen in the process.
Rip Hunter (Arthur Darvill) found Wally meditating in China and recruited him into the Legends of Tomorrow. Lonsdale joined the cast of DC's Legends of Tomorrow season 3 and Wally fit right in with the time-traveling misfits led by Sara Lance (Caity Lotz). Having a speedster on the Legends' side was a boon in their fight against the demon Mallus and his helpers Damien Darhk (Neil McDonough) and Nora Darhk (Courtney Ford). After they defeated Mallus, the Legends celebrated in Aruba before John Constantine appeared to present them with a severed dragon's head, alluding to the magical based threats they would face in Legends of Tomorow season 4. However, Wally left the series before the new season began; Lonsdale decided that he would step away from the Arrowverse in order to seek new acting opportunities.
Before Wally left The CW's shared universe he resurfaced in The Flash season 5 to meet his new baby sister Jenna and his niece-from-the-future, Nora West Allen (Jessica Parker Kennedy). He also traveled through time with a bassinet that belonged to Moses, which he gave to Joe and Cecile as a gift for their own baby. Kid Flash joined his friends one more time to defeat the rogue named Gridlock and to take some of Nora's DNA to the Legends for analysis before he left Central City and The Flash once more. Wally decided to run across the world but during the Weather Witch trial in The Flash season 5, Joe and his baby sister visited Wally in Tibet.
When Wally returns to The Flash in season 6, he'll once again team up with Barry to "fight one of the greatest Flash villains ever". Though it won't be a permanent stay in Central City, Kid Flash fans at least can look forward to Wally being back for "a few episodes". All in all, Wally West is a tremendous character whose potential has not yet been maximized in the Arrowverse so his return to The Flash is an exciting prospect, especially with Crisis On Infinite Earths looming on the horizon.