Lexa demanded that the Sky People leave her territory or die. Clarke Griffin instead offered a way to save both of their people imprisoned within the Mountain Men's fortress, Mount Weather, and Lexa agreed to a truce on the condition of Finn Collins's death in compensation for the massacre.

With their new-found alliance, Lexa and Clarke started working closely to free their people from Mount Weather. They grew closer and Lexa admitted to having romantic feelings for Clarke, though Clarke was not yet ready for a relationship. The alliance successfully took down Mount Weather's defenses, but before Lexa's army could attack, Cage Wallace offered Lexa a deal that ensured all of Lexa's people would be freed. In return, Lexa's army would have to retreat and never encroach upon the Mountain again. Lexa took the deal, saving her people but leaving Clarke and the rest of the Sky People to die in Mount Weather. After Clarke was forced to irradiate Mount Weather, the deaths of all the Mountain Men and Clarke's post-traumatic stress causes her to hate Lexa for her betrayal and for endangering Clarke's people.

Months after her betrayal, Lexa found herself struggling to maintain control over the Coalition; her rule being challenged first by Queen Nia of the Ice Nation, and then by Pike's faction of the Sky People. She also had Clarke brought to her in Polis amid the political turmoil. As Lexa worked to bring peace to the clans, Clarke forgave her and they became allies again and later lovers. Lexa's Flamekeeper, Titus, disapproved of their relationship

Clarke enters Lexa's room as Lexa comes into view

Lexa: When do you leave Clarke: Now. I'm sorry. Lexa: Don't be. You have to go back. They're your people. That's why I-- That's why you're you. Clarke: Maybe someday you and I will owe nothing more to our people. Lexa: I hope so. May we meet again.

Clarke moves forward and kisses Lexa and they have sex. Clarke and Lexa are in bed. Clarke is tracing Lexa's arm tattoo.

Clarke: If Octavia and I are gonna get behind the blockade by dawn-- Lexa: Shh Clarke traces Lexa's back tattoo Clarke: This is beautiful. Lexa: I got it on my Ascension day. A circle for every Nightblida that died when the Commander chose me. Clarke: 7 circles. I thought you said there were 9 novitiates at your conclave Lexa: There were Clarke: What happened to number 8? Lexa: Can we talk about something else? Clarke: We don't have to talk at all. Clarke and Lexa kiss