The core premise revolves around gender-swapped protagonists Fionna (female Finn) and Cake (female Jake), originally from fanfic-inspired AT episodes, which inherently promotes gender fluidity concepts but feels organic to the franchise's lore. A key progressive casting decision is rendering Marshall Lee (gender-swapped Marceline, voiced by Black actor Donald Glover) as explicitly Black in visual design, a change from his pale depiction in prior AT appearances; showrunner Adam Muto defended this as natural to match the actor and tie into Marceline's established Black mother, reflecting DEI-aligned voice-to-visual matching.

Prominent LGBTQ+ representation centers on the romantic relationship between Marshall Lee and Gary (gender-swapped Prince Gumball, voiced by gay actor Andrew Rannells), depicted with kisses, domesticity, and emotional arcs that integrate into Fionna's self-discovery journey, including queer-coded invitations to embrace identity. Simon Petrikov's arc delves into mental health struggles like depression and therapy post-Ice King, aligning with progressive sensitivity to neurodiversity and emotional vulnerability.

The show earned a ReFrame stamp for gender-balanced hiring and appears on lists critiquing LGBTQ+ agendas in kids' media. Audience reception includes some backlash calling it 'woke' for the gay couple, millennial angst over adult disillusionment, and perceived shift from pure adventure, though critically acclaimed and renewed, indicating elements enhance rather than overwhelm storytelling.