- Base-Breaking Character: Opinion on Youta is 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.
- 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.
- HSQ: 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.
- 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.
- 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 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.
YMMV / Parallel Paradise