The series premiere of “Adventure Time: Fionna and Cake” appeals to the now-grown fans of “Adventure Time” by involving old cast and character favorites and exploring matured themes and humor.

The new series premiered Aug. 31 on Max with two 30-minute episodes titled “Fionna Campbell” and “Simon Petrikov.”

In the rich lore of the series’ universe, Ice King creates the gender-bent alternate reality of Fionna and Cake to escape his loneliness.

However, the Fionna and Cake we meet in “Adventure Time: Fionna and Cake” aren’t quite as we remember them.

The first episode starts with a red herring to throw viewers off the sense of the plot.

“Fionna Campbell” starts with a pastel watercolor cityscape where a Sailor Moon-esque Fionna and her talking cat, Cake, chase down an evil Rat Car reminiscent of the Catbus from Studio Ghibli’s “My Neighbor Totoro.”

However, just as the audience is fooled into thinking the series would follow the same fantastical, action-packed fast humor that characterized “Adventure Time,” Fionna and Cake are whisked out of what is revealed to be merely a dream of Fionna’s.

When Fionna wakes from her dream, the audience finds that her reality is everything but fantastical.

Fionna wakes up in an apartment representative of every 20-year-old who doesn’t quite have their life together.

Having woken up to her sick and non-anthropomorphic cat, Cake, Fionna goes through her dramatically average day not fighting monsters, but dealing with the distinctly human everyday irritations, like working a dead-end job as a tour bus guide, struggling to pay rent and spilling coffee on herself.

This jarringly realistic setting sets the pace of the first episode as the show mimics the charming millennial sitcom style found in shows like “New Girl” and “Modern Family.”

Recognizing that the generation of existentially dreading youth “Adventure Time” created has grown into adults, the creators of “Adventure Time: Fionna and Cake” now cater to the audience with more mature humor, not shying away from the occasional curse word, gore and adult problems.

Despite seemingly not being in the “Adventure Time” universe, fans of the series quickly recognize the humanoid versions of beloved characters from the original series: Banana Guard, Hot Dog Princess, Crunchy, Abracadaniel, Lemon Hope and Cinnamon Bun just to name a few.

By the end of the first episode, dissatisfied with her average life that lacks the action-packed adventures of her dream world, and desperate to find out what is wrong with her sick cat, Fionna longs for a more magical reality.

The series’ second episode parallels the first: “Simon Petrikov” starts with a dream sequence as Simon, the human version of Ice King, dreams he is once again defending a young Marceline from zombies in the apocalyptic Ooo of the past.

When Simon wakes up, we find him in the familiar setting of “Adventure Time” in the period after the original series ends but before “Adventure Time: Distant Lands” begins.

Similar to Fionna, Simon too is dissatisfied with his place in the world as he struggles to fit into a futuristic society and grieves the loss of his lover, Betty.

The monotony and dissatisfaction paralleled by Fionna and Simon foreshadow a future of adventure as the audience awaits the imminent clashing of Simon and Fionna’s world and yearns to see how the “Adventure Time” story will continue.

New episodes of “Adventure Time: Fionna and Cake” will premiere every Thursday on Max.