18if

Both have mc dealing with a lot of people, each having it's own story that can sometimes be quite dark and dramatic. 

In both shows the mc stops "witches/mononoke" to keep those creatures from killing anyone. Also they get close to the creatures, finds their vulnerabilities, and sets them free. 

both trippy anime about a person diving into a different world that directly effects the real world and trying to save the people related to the respective "cases" (or witches in 18if) 

Both 18if and Paprika are trippy looks into dreams. If you liked the insane logic of one, you'll most likely like the other. 

I'm actually impressed no one made that recommendation yet. 18if and Bakemonogatari are both divided into arcs, each one following the same pattern : the male protagonist stumbles upon a female character who, because she is confronted to real-life problems, faces supernatural phenomenons. The protagonist then saves said character, helped by a specialist of these phenomenons (in the person of Lily/Meme Oshino). Friendship ensues. Also, both have particular art styles that make them stand out (that's especially true for Bakemonogatari). The protagonists have pretty much the same personality, same goes for the researcher of 18if and Oshino, and both are mystery/comedy/romance/occult anime. 

The ep 3 of 18if reminds me alot the plastic memories final. I cryed like as in Plastic Memories. 

•In both anime there are witches that create and then live in their special environments. •Both series are pretty gory and mature at times. •Both anime feature young girls in serious situations that might affect the real world. •Both series have interesting art styles. 

It has the same "dream" feeling to it. Be it the animation or the story, the "dream" feeling is quite similar 

The characters explore dreamscapes that represent various emotional states. The dreams range from the mundane or cartoonish to the emotional or horrifying, giving the shows a wide breadth of art styles. 

The same exactly concept: Solving young girls` problems in dreamworld. Both heavily use grotesque and surreal colorful artstile to picture the dreams and have distinguished arcs dedicated to one girl each. The only notable difference so far, is that 18if has a male MC.  

- Episodic - The MC digs around the character of the week wherein 18if, the MC tries to save her from the dream world, Warau salesman tries to make them have a deal with the devil - supernatural elements. 18if has the dreamworld and warau has his magical items. Both of them bring out their real character 

They are pretty much the same: - main character is related to/in a strange world and must fight witch-like persons, who are only in this other world, because they're desperate or sad in the real world - both seem pretty normal or soft at first, but they definitely aren't