- Adorkable: Beneath Lumi's proud paladin exterior, she is an awkward, goofy girl prone to cartoonish facial expressions and crying jags, and this is even outside of the times she's in heat.
- Base-Breaking Character: Opinions on Youta are split down the middle for many readers. Some fans consider him a refreshing change from the dense, nigh-gynophobic main characters common in Ecchi stories like this, and point out that despite being a bit of a jerk at times he's ultimately an altruistic, kind man willing to put himself in danger for people he's never even met because it's the right thing to do. Other fans argue that his willingness to have sex and his no-nonsense attitude are about his only good points, with the rest of his character considered either boring for resembling the beats of a Stock Light-Novel Hero, or Bastard Boyfriend material due to how he sometimes treats the girls.
- Big-Lipped Alligator Moment: During her first make-out session with Youta, Lumi starts lactating. Neither she nor Youta know why, they promptly forget about it, it never happens again in the myriad times the two of them make love in the future, and none of the other girls have it happen to them.
- Complete Monster:
- Kai is an immortal bishop of the Black Dawn, a cult that worships the God of Deep Jealousy. Fueling her immortality by consuming human gallbladders, Kai has spent millennia treating the seaside city of Lille as her personal feeding ground, ambushing those foolish enough to walk the beach at night. In order to strengthen her hold on the city, she sealed the land-bound goddess of Lille under the ocean, breaking the key into thousands of pieces and holds the final piece in secret in order to mess with the daughter of said Goddess. At one point, she has cursed the sister of Pinako, one of Lille's guardians, in order to force Pinako into becoming both the mole in the city and her Sex Slave. Once the existence of both herself and the god she worships is revealed, Kai then slaughters any civilians who discovered the secret. Paralyzing the civilians with a spell, she meticulously stabs them through the chest before transforming into the monstrous Cetus in order to fight with Lumi and the other guardians. Beating them to within an inch of their lives, Kai offers to spare them in exchange for loyalty, only to try to kill the one who accepts her offer regardless.
- Galia is another member of the Black Dawn who disguises herself as a Sendario Resistance member before dropping the charade and cursing Katsuchi to mate with a fellow Resistance member or debase herself in front of everyone, with the humiliation so grave Katsuchi nearly kills herself. Returning later, Galia restrains Resistance members while she butchers and devours them one by one, consuming them all before heading to the city of Mies where she murders a group of girls and tries to force them to surrender one girl each day for Galia to eat lest she kill everyone living there. Even when mortally wounded, Galia jovially taunts Youta about the coming arrival of the destructive God of Deep Jealousy.
- Fandom Rivalry: A nasty one with World's End Harem, due to their similar premises ("ordinary" man stuck on Lady Land has to have sex with an array of women for plot), and in general arguing about which series is superior.
- Hilarious in Hindsight: There's a meme where hand-holding is treated as kinky and NSFW. Cue this manga, where the girls go into heat at the slightest touch, including hand-holding.
- Memetic Mutation: An unfortunate fanslation error resulted in this, during a sex scene no less: the translator forgot to fully edit one of the word bubbles and left the placeholder in, resulting in Youta staring seriously down at a panting, flushed, hopelessly-in-heat Pinako and saying "Text" with no punctuation.
- Moral Event Horizon: While his behavior became increasingly muddied as he stayed in the fantasy world, Youta eventually crosses this with his treatment of Mai, in which he tricks her into having sex with him under the guarantee that she'll avoid moon breaking, when she doesn't even know what sex is and he's already figured out by that point that sex isn't guaranteed to save a girl.
- For a lot of people, if he didn't cross it then, he basically crossed it when he functionally RAPED Nakuta, the head of the Empress's royal guards, in order to force the band on her neck so that she would have no reason to continue to follow the Empress's orders to kill non-virgins. Though he was driven by the idea that this would remove her as a threat so they wouldn't have to kill her, it probably doesn't have to be explained why a lot of people had a problem with it.
- The Scrappy: Erza, who quickly earned the ire of much of the fanbase by torturing and humiliating Youta. Despite the clear attempt by the author to garner sympathy as she dies from Moonbreaking, a good percentage of the fanbase isn't buying it.
- Shocking Moments: Sendorio. Sendorio is just one HOLY SHIT moment after the other, culminating in the long-awaited reveal of the God of Deep Jealousy. In that moment, that one shining moment, it's revealed that the whole time, Lynn Okamoto has been playing the reader for an absolute idiot. In that one moment, Parallel Paradise becomes the Isekai equivalent of Metal Gear Solid 2: Sons of Liberty.
- Squick: Readers who aren't fond of the girls' secretions will often think this way. It's a thick, odorous substance that flows out in liters whenever the girls get horny. Many a fan commented that those secretions took away from the sexiness of a scene.
- The Un Twist: Few, if any readers trusted Arara, and people were guessing she was Galia from her introductory chapter. Sure enough, they were right.
- What an Idiot!: Okay so Youta basically raped Nakuta to remove any reason for her to follow the Empress's orders. He decides to release her from the dungeon afterward. Ill-advised, but fine. However, instead of having the guardians of Sendorio do it, while armed, and with her under constant watch, he goes to release her himself, alone, unarmed, with no backup forthcoming. He's then actually surprised when she punches his lights out, kicks the shit out of him, and threatens to kill him anyway, and its only then that he realized that releasing a powerful warrior he sexually assaulted, and assuming she had no reason to kill him, was probably not the brightest idea he had. The only reason he isn't dead is because she decided to not take revenge.
YMMV / Parallel Paradise