Fantasy Bishoujo Juniku Ojisan to

Its gender bender isekai. What else 

Basically both animes have a similar main quirk, that being the main characters are desperately trying to not show their obvious attraction to each other and trying to get a confesion out of the other, while a third party (fujiwara/ goddess of love and beauty) is ocassionally meddling with their plans. Both animes are in the comedy genre, the main difference between them would be the settling, kaguya follows the highschool slice of life pattern and have no supernatural elements while bishoujo takes places in another world filled with magic and fantasy elements 

Fantasy Isekai comedy series that both take the piss out of the genre while having really great chemistry between a group of loveable core cast members 

Both have gender bender where the "girl" starts to swing that way 

Both anime have a particular view of isekai which is full of comedy! They make fun of stuff that is common in isekai worlds getting almost ridiculous (exaggerating things for example) and both have a refreshing way to portray that. If you like any of these anime, then watch the other because you will have the same fun.  

They both have a similar plot of two best friends/rivals where one gender swaps and they try not to fall for each other. However, Kuro Gal ni Natta kara Shinyuu to shitemita is smut, so please be advised. 

Not only does the main character Gabriel and Tachibana from each anime look extremely similar, the side characters also have a similar vibe to them depending on their intelligence and knowledge level. Although two completely different plots, the characters appear almost the same in each anime. By watching these two, it is almost like looking at a mirror at how the characters would continue to play out the story line due to their similar nature and both feature good character development for their characters. Thus, if you like one, you should also like the other.  

they give off the same vibe and they're both really funny  

While one is a gender-bender rom-com isekai and the other is a parody of the shonen/superheero genre with a focus on the protagonist's mental health, both shows feature a comically OP MC who's OPness is often a source of comedy during action. They also have very similar comedy styles making fun of their respective genres. 

They both star two close friends, one of them gets gender flipped, and there's a lot of humor in which the other starts questioning their feelings for the one gender flipped. 

Both plots have nothing in common, but the comedy of both shows share similar feelings, Gintama is a Classic, Fantasy Bishoujo like Gintama has no direct objective of path to follow, like early Gintama Fantasy Bishoujo is entertaining without puzzled yourself figuring out what’s going on or happen 

Two rom-com fantasies with characters transported from the real world to their fantasy settings. Circumstances are different where in Hamefura, the main character is isekai'd due to death but transported to the setting of a visual novel she plays. In Fabiniku, two main characters are transported just like that by some Goddess but one of them undergoes a change. Their plots differ a lot but perhaps the most similar aspect is the amount of comedy they have balanced out with wholesome moments but I would say Hamefura is more regal in approach and Fabiniku is a lot more hyper and faces more towards comedy compared to. 

Both shows focus on jokes about boomers being trapped in isekai, with the only difference being that in one show the characters are in isekai and in the other they have already returned from another world.  

1) Both have a lot of 'hectic' humor. 2) Both parody RPGs. There's also the fantasy world, having two protagonists, and even sharing the common old premise of beating the monster lord. The only significant difference is that Mahoujin Guru Guru is a little more story oriented. 

Just like Fantasy Bishoujo Juniku Ojisan, Gonna be the Twin-Tail!! is also a comedic series where the protagonist gets gender bent, Mitsuka Souji might be able to switch back and forth but the way some of his friends react to the changes come into play frequently, you will also find a lot of similarities in the sense of humor that both anime use parody their respective genres, Fantasy Bishoujo with isekai, and Twin Tail with magical girls.  

The main gist of the series are rather similar - a guy turns into a cute girl and in both cases are treated as "curses". The rival of that guy either liked the person already previously or starts to have feelings towards the "new girl". However, Tenshi na Konamaiki is not isekai while Fantasy Bishoujo is.  

Jail- Licht, Tachibana- Jinguuji, similar comedy, isekai