Kage kara Mamoru!

Both have a very simular theme based around a boy samurai or ninja who is surrounded by girls, clueless to the fact that one or more like him. Nijuu Mensou is probabbly geared more towards girls, while Asu no Yoichi is geared more towards boys... and has panty humor in it. 

both series' protagonists wears glasses and are romantically linked to their pink haired heroines plus in koi koi 7, the heroines led by the female lead protects the male lead. in kage kara, the male lead protects the female lead 

both series have sword wielding girls (motoko and tsubaki), both series' male protagonists wears glasses, and are romantically linked with the female protagonists and both female protagonists even sang onscreen 

Both have a guy to protect a girl and its fantasy with romance 

The male lead in Kage kara Mamoru and the female lead in Kaichou wa Maid-sama both have secrets that they try to keep hidden. Both are comedy, romance and in a high school setting. 

The main characters are both childhood friends and like each other. 

Both are comedy and have female samurai characters (martial arts), fighting scenes, and a boy surrounded by girls (harem). Both are comedy, romance, and in a school setting. 

The male lead, Mamoru in Kage kara Mamoru has a secret, same as the main female, Subaru in Mayo Chiki. The male leads in both shows, Mamoru and Kinjirou are also surrounded by females, in a harem. Both anime are comedy, romance and school. 

Similarities: Both anime deal with martial arts and ninjas, a guy wanting to protect a girl yet has his own harem. Difference: Oda Nobuna no Yabou is set in a historical time-frame and Kage kara Mamoru is set in a present time.  

It is basically the same series, just replace ninjas with mages. The difference is that in Kage Kara Mamoru the main hero knows about his talents in opposite of Magikano, in wich the hero awakens to his. Both series aired in the same cour. 

To me, the tv series and the OVA had a simular humour style and both had quite a bit of action to it. 

Kamichama Karin and Kage Kara Mamoru have a similar feel. Both have a slightly clueless girl, who is protected by a more able guy. Karin is a little bit more apt than Yuna. Both shows have similar humor, but Kage Kara Mamoru is about ninjas while Kamichama Karin has a more fantasy feel to it. They are both excellent and definitely worth watching. 

Both have very koi female lead characters, who are rather naive about certain things. They also have anime figurines in the show. Both shows are rather simple, rather sweet, mild story line that is rather relaxing. 

In this comedy a ninja protects a clumsy moron they are in love with. But this time the ninja is the female and the clumsy moron is the male. Think of this anime with a role reversal. Same very cute romantic comedy of ninjas and their accident prone love interest. Himawari protects her teacher whom she is CONVINCED is a skilled and wise master, in reality he is an incompetent boob but her love goggles won't let her see that.  

A comedy about a highly skilled ninja who attempts to protect an accident prone moron of a high school girl. no love story here and plenty of tits but same basic premise and LOTS of hilarity. Mainly boob and panty jokes though on this one. Still if you like ninja protection comedies this will float your boat 

rolls reversed here. Young ninja perfecting his skills protects his clumsy moron love interest. Kinda like this except the male and female rolls are reversed. I prefer mamoru to this but it's a close call and they are very similar. If you like ninja protection comedy romances this is the next logical series for you to watch. 

both animes feature a guy who's surrounded by many girls and they all have feelings for him... but kage kara mamoru has a ninja setting and rosario + vampire has a monster-ish setting