R-15

Similar humor,both are random and funny :D, both have a touch of shonen ai between the main characters, similar art. 

Both involve underaged teens working questionable jobs in the porn industry, with Koe de Oshigoto featuring a 16 year old girl as an eroge seiyuu, and R-15 featuring a 15 year old boy as a porn story writer. These cause humorous interaction between the main characters and their peers at school. Both also contain visuals of the main character's perverted imaginations, though Koe de Oshigoto's border on the verge of hentai, and R-15s barely qualifies as ecchi. 

Both their schools are weird, are harem , and have many ecchi scenes here and there. 

A male lead surrounded by big tittied high school girls. These anime will not challenge your mind or offer any worthwhile experience. However, breast and panty shots galore await you. 

The idea of the main characters writing stories that can be seen as lewd and daring, while also dealing with female characters that can also be looked at also lewd and daring 

Tsuki ga Kirei and R-15. Both have the following similarities: - A girl and a boy, they feel attraction of each other, which in turn, have friends who feel something for them. - Both boys have some talent, the boy is a writer and the girl is musician (R-15) / sports woman (TgK). As we go through the chapters, we see how the protagonists get to know each other, and gradually show what they feel, despite creating misunderstandings. 

Both series are about Masters of their craft without equal in a High-School setting. R-15 has poor art compared to Saenai Heroine no Sodatekata, but if you can look past that I think that if you enjoyed one series that you will enjoy the other.  

Both series depict the everyday life of ecchi writers and how they struggle to meet their deadlines while also keeping their wild fantasies in check. 

The main characters, Akito (Oni Ai) and Taketo (R-15), write erotic novels as their hobby and their unique talent. They have similar humor and belong to the same genre: comedy, ecchi, romance, and harem. They also have unique characters with different talents and personalities, and character and story developments are slow paced for both anime. 

Similarities: Both muchachos (male lead) are genius in their own right. Both muchachos wore ridiculously looking school uniforms. Both have a side kick with a rather unusual sense of loyalty to them. Both muchachos deals with women with their own unique problem and trouble also awaits them along the way . Both have school, harem and comedy genres in them. Dissimilarities: Though both animes have school genres in them, one is set in a specialize high school for geniuses while the other one is set in an ordinary high school. When it comes to school uniforms, in R-15 the girls wore beautiful looking uniforms, while the boys sport kind of uniform that makes them look like a butler. In the other anime 'Kami nomi zo Shiru Sekai" both boys and girls wore very overly decorated 60's kind of attire. One has ecchi and romance as it's extra genre, while the other has demons and magic as it's extra genre. The muchacho in one anime has a love interest, while the other maintains a lot of relationships whom are all virtual girls in his dating sims via "PFP" (or PSP for that matter). Lastly, one is a true harem, while the other is a pseudo harem.  read more 

The stories are both set around individuals with abnormal talent. They both have lots of comedic relief... Well. I don't know why I'm reccomending this. I just am. Trust me. 

There is a similarity between R-15 and Danganronpa which is the characters, the characters from both series are the best of their type, i.e. Geniuses and both main characters have ability which would be considered out of the ordinary. 

They both portray a harem theme. Isekai no seikishi monogatari is an amazing anime with almost an hour length per episode. R-15 not the best harem, but you can watch it if there is nothing left to watch.  

MC wins girl's affections by making somewhat smart speeches. Both are harems. Both are somewhat ecchi.