Tsuki wa Higashi ni Hi wa Nishi ni: Operation Sanctuary

both have girls from the future 

Similar female characters around the main lead with time travel aspect in both. Both also have that kind of drama that comes with these types of anime.  

In both animes there are a lot of girls and one guy interacting with them. There is also some romance and both are set in a high school.  

Clannad and Tsuki wa Higashi ni Hi wa Nishi ni -Operation Sanctuary- might be similar in it's story and such..Operation Sanctuary or also known as Hani Hani and Clannad are very similar with the Characters and Story..But Clannad has more Drama^^ (Similarities:) -Characters <== Look/Appearance,Attitude,Habits etc.. -Story <== Life -Genres <== [Well you guys will know that!] In Hani Hani the characters are not really that good in acting but in Clannad the characters are well rated :) But Hani Hani has a good life story as well ;) so does Clannad.. Clannad is a Famous/Popular anime as you can see but Hani Hani is not..So probably you think Hani Hani is not that interesting but I fully recommend you to watch Both..Or if you have already watched Clannad then watch Hani Hani or if you already watched Hani Hani ahh Duh watch Clannad! I am sure you will like both stories :) Also,you will notice many similarities!Just watch both if you want to know ;) read more 

In both of these series the characters are very standard and are rather recycled. That's the first similarity I noticed. The second is how long it took for the main guy to admit his feelings for the main girl. Also, the main girls are so pretty! Both are laid back series and are generally a nice watch with storylines that aren't too intense ;3 

In both anime the main character has lost his parents and his memory when he was younger, but starts remembering things when he meets a strange girl who seems to know him.