Asobi ni Iku yo!

Very close, both of them have aliens and a lot of ecchi moments with a bit of action. 

Both are ecchi/harem anime with high school male protagonists surrounded by supernatural (Omamori Himari)/alien (Asobi ni iku yo) females. Both anime also have some fights.  

a female came down from space and the the male protagonist romance in both anime 

clueless airhead alien coming to earth and it seems everyones ok with it  

both involve a regular guy getting pulled into a cat world the main guy also has a childhood friend that likes them they both have a decent amount of comedy in it and there both harems so they have those generic episodes like the pool/beach one and the onsen/hot-tub one. 

Wars against cat people and dog people, but asobi is kinda ecchi ... more like alot. 

Both have female "aliens" with incredibly advanced technology, abilities and weapons, who meet a guy in Earth. Also, the guy (and his friends) get involucrated with a dangerous organization (like Synapse in Sora no Otoshimono). 

They're both harem series with multiple types of girls liking the protagonist, who is very unaware of the situaion. Besides that, both of the main character girls are from space, big chested, wear tight space suits and have small helper(s). Both series have ALOT of fanservice as well as a somewhat similar art and story. 

Guy living with catgirls that can be somehow confused about how the human world works sometimes. Both are mainly fanservice series, but while Nekopara has cute-centered fanservice, Asobi ni Iku yo has ecchi-centered fanservice. 

Also sci-fi, comedy, romance, a female alien and the male character look similar aswell. 

Highly capable young ladies in skintight suits making the world a better place through the copious use of surprisingly non-lethal high-tech gear, and the male teenager whose trousers they all want to get into. 

Romance comedies with a lot of girls after one boy. Oh, Kampfer character appear in the background of episode three of Asobi ni Iku Yo. What? 

Sudden Girlfriend appearance anime who is weird in more ways than one. Kemeko is more comedy than romance though, and is lacking in the alien department.  

both anime center around a normal guy that has a supernatural/ alien girl/woman crash into his life. both are lighthearted anime with some dark undertones and both are somewhat slice of life anime with a twist. differences in Cat Planet Cuties (CTC)the MC is a high schooler that meets the alien cat girl at a family function. in Helpful Fox Senko (senko) the MC is a salaryman that come home to find the demi-god fox in his apartment cooking him supper. CTC has some political drama, more action, as a lot of ecchi scene and a harem. with the MC and cat girl being near the same age. Senko is a more traditional slice of life with the MC and demi-god fox relationship being up in the air as she 800 and he late 20s early 30s  read more 

The same ET girl and earth boy kind of romance, comedy and some ecchi, however in one anime the ET girl there was open for his earth boy to have multiple realtionship and the Earth Boy was more like a reserve kind, while in the other anime the earth boy there is a pervert and his ET girl is a yandere kind.  

A lot of similar characteristics, even if the actual shows are from relatively different genres. Both involve girls with animal ears and tails, with a lot of fanservice and ecchi, and then also aliens and sci-fi concepts, with some pretty good action scenes. 

Asobi is Highschool dxd meets Spice and Wolf. if you like ecchi comedy parodies, Asobi is a great choice. Conversely, if you enjoyed Eris but want to see what she could be like if she were a little more serious, Holo is exactly that. 

Kinda similar humor and both are good series so if you need to laugh hard you should take either one ;) 

Macademi Wasshoi is essentially Asobi ni Iku yo reimagined with Gods, Demons, and Magic instead of Cats, Dogs, and Science. It has the same humor, the same character archetypes, the same animal-eared themes, the same ecchiness, and the same pop culture references. If you like one, you'll like the other. 

First off you should note that both of these series are not ones you should watch for the plot, because they are absolutely pointless. now on to what most people are looking for, the fanservice and types of characters both have harems, useless mc's, a childhood friend, and most notable to these animes, actual animal hybrid girls. we arent talking your typical cute maid cafe cat ears and tape on tail. no we are talking serious bidness cat girls and other less interesting hybrids like rabbits n dogs the fanservice in both of these is really prevalent, though in asobi there is not as much nudity, but it is just as suggestive in terms of fanservice. be prepared to see at least three panty shots every thirty seconds in usagi, with a suggestive line in the middle of them to add even more interest to the main point of the show other than that if you want to watch some mindless fanservice without having to worry about a plot then these are for you!!!  read more 

Moe+Harem+Military Asobi ni Iku yo has a nekomimi and a stronger military theme while Ninomiya-kun has a succubus theme. 

Random but funny plot. A lot of action and ficton, harem and just a bit of drama. 

An alien girl comes to the Earth and falls for the protagonist, other girls come into the picture and a harem ensues. Lots of action, sci-fi and ecchi in both ones, not forgetting the comedy. First series coming to mind when watching Asobi Ni Ikuyo was definitely Nyaruko-san. Also, both protagonist alien girls having something to do with cats. 

The similarity can be looked at the High Level of Militarism, that will revolve around both the protagonist and the alien-heroine. Secret Organization, Alien Cults and Secret Government Military Agents. Alongside with mild ecchiness and a Web of Love Drama. 

They share the same comedy + ecchi based story style Both have some missions and the actions are mainly performed by young female. Asobi ni Iku yo is more random. It is bundled with UFO & catgirl aliens, with a protagonist and a harem; while Aika is female centered with a secret mission to complete per series...  

Both are romantic ecchi anime, with girls who are not from this world. In Chobits, the main female character is a robot (aka persecom). In "Asobi ni Iku yo!" the main female character is an alien. They both have to learn the things in life. Both girls are being helped and live with a male character. 

Fan-service and sci-fi action. If you're looking for both of these genre, then these two series might be something worth checking out. The lucky or maybe unlucky protagonist gets into situations involving the girls and later forms bonds with them through the series. It does have a story plot though so keep an eye on that. There's also comedy, drama, and action. And here it is again: fan-service. 

Same Genres and about a wolf /human 

Similar alien comes from outer space and changes main character's life. Both shows have a bit of a similar light feel but at times have action. First thing watching this it reminded me of the other show perhaps its something in the animation or music that is great. 

Although the two are about two entirely different things, Nyan Koi! about cats, and Seto no Hanayome about mermaids. However, both have similar genres like they're both romance-comedies and harems. Also both involve the main character getting into some sort of life threatening danger.