Oniichan wa Oshimai!

Both of these shows have a peculiar mix of wholesome feels with lewdness. Both also involve a fantasy element entering the main character's life (gender swap/dragons) and them adapting to their new circumstances the best they can. 

Both are created by Studio bind with a similar art and animation style. Both involved a shut-in NEET man becoming a child, and was given a second chance in life. Slowly but steadily, both slowly integrate themselves back to the society,  

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

Both are slices of life containing the daily life of lazy and hard-working siblings and have a moment of heart-warming sibling love. 

Both of these anime have the similar plot of the protagonist getting aged down and returning to school to change the path of their lives, after living life as a NEET. OniMai shows this off as a comedy, while ReLIFE explores this in a more serious and philosphical manner. 

Female protagonist of Watamote acts a lot like the protagonist of Oniichan wa Oshimai, minus the gender bender factor. Is a degenerate. If you like tiny girls that act "gross" then watch this too.  

Both series have main characters that going trough gender change and struggles of understanding what is the meaning of belonging to a gender. Nitori is officially a trans girl and she had her own struggles in a similar fashion. Horou Musuko is more realistic and a bit darker than Onimai, due that Onimai being a comedy show. If you are into exploring the trans issues I’d recommend both of them. 

People are asking me, how come im comparing a fantasy comedy anime with a moe comedy anime? It’s really bizarre seeing that. Yes, It seemed unusual at first, but secondly, there are very alike. What im saying alike, Mahiro and Yamada are guys who dont really achieve well in academics, has another person who is a better role model than them, and they play around in a girl’s body. The difference is that Mahiro has transformation while Yamada can switch with another person either as a girl or a boy still. It still has those misunderstandings, panic moments and Fan service there still. 

Both goes about someone getting into a life they don't want to get into and need to learn to live whit it. 

Both animes centering around an elementary school group of friends and an older sister! Both an anime to just relax too and enjoy the fluff and cuteness of the simple school life. Both animes include the cast of cute girls doing classic elementary activities like culture festivals, and home etc. baking. 

Both have yuri elements with an exploration of sexuality. 

Both anime are CGDCT anime with lots of comedy. The main characters of each anime are also quite clumsy in different ways and go through character development as the series goes on. If you enjoy one anime, you'll probably enjoy the other too. 

Both of the male mc's were forced into becoming female by their sisters. 

romcom about little sister complex 

It is a surprise how much of shoujo ai + slice of life both of these anime share. 

Boy transformed into loli girl. Similar humour.  

Both involve the main character who was originally male being forced to live as a girl for one reason or another, while Onimai is a full change to a girl Himegoto is just (very persuasive) crossdressing though. They both have a large portion of comedy but Onimai is able to build a more coherent story and do more in story/drama aspects since it has a full season while Himegoto is a short. I'd say if you enjoy the concept of genderbend in general you will probably enjoy both shows. 

Both anime are about the recovery of a hikikomori. NHK goes in a way more dark and dramatic, and we get to know other people with other problems Onimai goes more in a comedic and soft way. 

Both have similar art style as well as share the same producer and themes (CGDCT/School). Girls becoming friends by joining the same club.  

The main characters of these series are extremely similar because they are both a shut-in and happened to become a girl overnight, so both of them has to deal with these changes in their life and there is a character that helps them. Both are comedic and has a lot of fanservice.  

Watching Onimai was like watching Shinonome Lab residents and their guests for 12 episodes, except there was no talking cat in it. Some soundtracks in both shows are composed in orchestra style, and the one song that plays in some episodes in Onimai is basically an arrangement of "Green Green" song, which was the ending theme in EP 18 of Nichijou. The animations and drawing styles are both distinct and cute for comedies and pastel colors add some wholesomeness to them. Nichijou and Onimai conveyed a kind and relaxing feeling to me in a similar way, and in my opinion, if someone is deserved to make a sequel to Nichijou, this would be Studio Bind. read more 

After i heard the reason behind why Mihari transformed her own brother as a cute little girl, my first thought instantly jumped up onto oreimo, since they both kind of share a similar bonding sister-brother background character history. Little sisters were a prodigy while the brothers were a complete up-to-no-good person that needs to be fixed by their own sisters. Ofc they both, which refer to also both sisters and brothers, had their different approach to comprehend the situation, which also differentiate by how they flow the bigger image of their story toward the whole story. I recommend to watch this two.