Ane☆Haramix

When I watched this Hentai I kinda got the same impression. Both protagonist end up having sex with the mythical character (Shinigami or Goddess). If you liked Namaiki: Kissuisou e Youkoso! The Animation you will also like Ane Haramix. 

The same plot where guy gets to bang 2 girls, though one has the 3rd girl who come around, both guys did a virgin.  

The same kind of threesome where it involve a guy with 2 girls in the helm, except in one anime it involves guy with 2 step sisters , while the other one involves guy with 1 older sister and one hot demon.  

Similarity : Both hentai tell story about love & sex between sibling Different : - In haramix MC must making sex with his sister because that was the only way to save his live from death - In Swing Out Sisters, MC making sex with his sister just because "love" 

First Love is 3 Episode OVA with 3 Different Story & 3 Different Couples If you like love between siblings, I recommend you to just watch the first episode of First Love which focus to love story between kasumi & her brother 

A succubus seduces,transforms,has fun with a guy what else could you imagine 

Both have a succubus ,in which he flirts and have fun with her,make out with other girls  

Love triangle...  

Both series have the main theme of main female characters that need to become pregnant in order to save the man male character from some type of calamity. In the case of Ringetsu, It's to protect a inheritance & future social standing & in the case of Ane Hara-mix, To extend the main male character's life.