[[folder: Fridge Logic ]]
* Xenovia's intention is to bear Issei's child. [[DidntThinkThisThrough So why is she carrying around condoms?]]
** She only directly tried bearing his children in the episode she surprised him in - Issei's freaked-out reaction was summed up as (paraphrased): "Do you understand what you're saying!? You wanna make a baby!? That's insane! That's insane! That's insane!". And not only that, this attempt indirectly caused agony to Issei, due to the beating that resulted from the misunderstanding (something she certainly wouldn't seem to be all for). So as a result, she likely decided to put the baby-making on hold for now until Issei said/showed it was okay - hence the condoms, and the 'we can practice anytime' aspect. Becoming a Devil also means she's got plenty of time to wait now, since most live 'almost forever'
[[folder: Fridge Brilliance ]]
* Sirzechs in the last episode of the anime seems content that Issei took Rias away from the engagement ceremony and even Grayfia notes that he seems happy about the fact that it's "unfortunate" that the Gremory and the Phenex clan will not have any marriage whatsoever. The reason why he's happy about it is [[spoiler: because it reminded him of his and Grayfia's circumstance when he married Grayfia, one of the servants of the Old Lucifer and at that time, it was a big no-no.]]
* Cao Cao being CrazyPrepared in general but especially Volume 11. Let's face it, if you were a PlayerCharacter and you're up against an armada of demons and angels and you're target is to take the power of the strongest dragon aka your PuppetKing, wouldn't ''you'' wanna be CrazyPrepared for the situation by collecting all the [[InfinityPlusOneSword Infinity Plus One Swords]] and an assortment of [[GameBreaker Game Breakers]] just to even stand a chance against them? Even Azazel notes that they're the [[FinalBoss Final Bosses]] for the humans in video game terms.
[[folder: Fridge Horror ]]
* Issei DoesNotKnowHisOwnStrength. Normally this can be shrugged off as HeroicSelfDeprecation, but during the Mid-Class exam he attacked another low class devil (who may or may not have had the power to become mid-class) in Balance Breaker. If he had boosted at all, he would have blown the other person, ''an ally'', in two.
* [=CaoCao=] implants himself with a [[TakenForGranite Medusa's eye]] to replace the one Issei shot out. What happened to the Gorgon?
* Issei's motivation is to become a high class devil so that he can gather a harem of female servants that he can have sex with. He essentially wants to become a SerialRapist that constantly engages in SexualExtortion of his subordinates and nobody has called him out on this or even noticed the UnfortunateImplications of his goal.
** Unfortunate implications aside, Issei has proven through his interactions with the girls that surround him that he is respectful of the girls as individuals with their own thoughts, feelings, and ambitions, proving that you can lust after a woman but still understand there is a person underneath that physical beauty. Hell, Issei has even outright rejected the (often times aggressive) sexual advances of the girls surrounding him because of some issue that led him to believe it was inappropriate at that time. This track record would lead us to believe that even if he had his own servants he wouldn't abuse them.
** Not to mention the fact that one of the first big fights was against [[ShadowArchetype Riser]] shows that Issei does truly value the feeling of each woman unlike Riser who does it just to have women. In summary, Issei would never force someone to join his harem or to have sex with him: his ultimate dream is to have a bunch of women madly in love with him of their own choosing. Purely consensual relationships all around.