The Umbrella Academy season 2's Klaus storyline subtly shows the Hargreeves family's spiritual medium overcoming his childhood trauma. Growing up with superpowers is never easy, but the experience becomes infinitely harder when your father is an emotionless taskmaster hellbent on raising the perfect superhero team. Sir Reginald Hargreeves scarred each of his adopted children one way or another, but Klaus was arguably treated the most cruelly. As part of his "training" Reginald locked Klaus in haunted crypts filled with ghosts, hoping the young boy would learn to control his power. And he did... by abusing alcohol and drugs to numb the spectral voices and block out his trauma altogether.
From one perspective, Robert Sheehan's Klaus experiences a regression in The Umbrella Academy season 2. After going cold turkey in Vietnam and falling in love with Dave, Klaus seemingly overcomes his demons by The Umbrella Academy season 1's finale, harnessing his true power to fully manifest Ben's ghost for the first time. However, Klaus' alcoholism returns in season 2. The Seance once again finds himself down and out at the bottom of a bottle, and making all the bad decisions that come along with his addiction.
Though Klaus' journey in The Umbrella Academy season 2 could be interpreted as unwinding his season 1 character development, a hidden storyline suggests Klaus is actually facing his demons, in spite of the relapse. Sir Reginald's graveyard torture sessions understandably leave Klaus struggling to build trusting relationships in The Umbrella Academy season 1 - even with his siblings. Klaus has no real friends, and pushes the other super-powered Hargreeves kids away at every opportunity, including the ghost of Ben. Meeting Dave in Vietnam represented the turning point that helped Klaus clean up his act, but then Dave died on the battlefield, and Klaus returned to his native 2019 timeline.
When the Hargreeves siblings are collectively warped to the 1960s by Five, Klaus is maintaining sobriety. Nevertheless, The Umbrella Academy season 2 proves those deep-seated traumas haven't gone anywhere. Klaus exploits a rich old woman and surrounds himself with cult followers who hang on his every word. Klaus' lifestyle is a narcissists dream - a mansion full of zealots who'll do anything he requests. But The Seance becomes so tired of this meaningless adulation, he ends up running away from his own cult. The whole experience proves Klaus' original problem of foregoing meaningful relationships and pushing people away is getting worse, not better, and being spurned by a past-timeline Dave is the final straw that sends Klaus back to square one in The Umbrella Academy season 2.
But, if the theory holds, this is where Klaus Hargreeves' true recovery begins in The Umbrella Academy. Unable to fill his emotional void using a crowd of besotted fans, and without Dave by his side, Klaus finally takes the path he should've chosen long before - he turns to his family. The latter episodes of The Umbrella Academy season 2 find Klaus semi-broken and back on the sauce, but closer to his siblings than ever. Luther, Diego, Allison, Five and Vanya were always the five people in the world who could understand Klaus' traumatic childhood, but only in The Umbrella Academy season 2 (beginning with his joyous Allison reunion) does he stop closing them off emotionally. Maybe Klaus needed to go through the cult, Dave's rejection, and an addiction relapse to finally bring down those walls.
Whatever interpretation you prefer, Klaus Hargreeves can now become his best self in The Umbrella Academy season 3. Reginald once hinted at how Klaus has barely scratched the surface of his seance potential, and having laid his ghosts to rest (quite literally), the psychic vagabond is finally ready to prove himself in The Umbrella Academy.