To thwart Morgan Edge, Lena buys Cat Co. and becomes James' boss. The two oddly clash in the beginning, with Lena being somewhat acerbic to James and dismissing his hitherto leadership structure, instead of merging it with her vision into an easy transition for the company. James is understandably irritated, but they eventually find a truce when Edge claims Lena is responsible for poisoning children with the lead bomb. Lena gives a press conference to clarify the situation and James protects her when an angry parent opens fire on her.
Lena thanks James for saving her life and they seem to start anew on good terms in their working relationship. Around Christmas time, at Kara's Christmas party, Kara and Sam tease Lena that she and James' chemistry is evident to everyone. Lena says it's complicated, because she's his boss, but they continue flirting and later share a kiss. Following the kiss, Lena wants to talk about it, but James is dismissive as Kara is in a coma and he's preoccupied, which Lena takes as his hesitance to get involved with a Luthor due to his close friendship with Clark. She confesses this to James, who assures her that he does like her.
James stands by and helps Lena when Morgan Edge's life is threatened and he accuses Lena of being the culprit. He goes with Lena to Edge's office where she tells Edge off and James backs her words with his own. Unbeknownst to James, Lena goes on her own to Edge's office and holds a gun to his face, threatening to shoot him. Lena and James continue dating, but their relationship is put on pause when Lena realizes that Sam is Reign and starts trying to help Sam without telling anyone else what's going on. This has her dodging a puzzled James's calls, but she assures him she's still interested.
When Kara gets unsure about Lena, she asks James to check out whether Lena has more kryptonite in her vault, which puts him in an uncomfortable position. Although he's continually effectively lied to Lena about Kara's secret identity, it also is not his secret to reveal. At the last second James decides not to enter the vault and lies to Kara, saying he did and there's nothing there. This comes across as James trusting and caring for Lena, not wanting to betray her trust and not wanting Lena and Kara's friendship to be jeopardized. James decides to reveal to Lena that he's Guardian. He tells her what he did and apologizes, saying that he trusts her. She responds with giving him her trust and tells him that it wasn't Lex's kryptonite they used, but hers, as she found out how to make it.
From then on they become a team and support each other through everything. James still hasn't told Lena who Supergirl is, which is likely to have severe consequences for their relationship once she finds out the truth.
It's a common ship as they became canon in Season 3 and stayed together for most of the season, and is currently the only romantic relationship on the series. However, the ship is somewhat divisive in fandom, due to the poor handling of the Kara/James canon, and the popularity of the Kara/Lena pairing. There seems to be three common reactions in the fandom to this ship:
- Some feel it's another jab at the unresolved Kara/James pairing, as well as a way to downplay the Kara/Lena ship and interactions.
- Some ship it.
- And some root for this development to eventually give way to Luversen (Kara/Lena/James).