Himawari!!

both have ninjas getting stronger to protect ones they love/care for 

Both animes are about ninja girls training in ninja arts and doing funny things... 

Both are sequels to anime full of ninjas! 

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. 

Just like the original himawari it and shinobuden it focuses on the life of an incompetent modern kunoichi with a lot of heart always making an idiot of herself. If you like shinobuden this is a little more plot but not much and really hilarious. 

Both Anime have elements of comedy, but Gintama's comedy is a lot better. Where Himawari!! ends up in averageness, Gintama goes all-out and makes you laugh really hard. Also both Anime somehow share other similarities (Ninjas and Samurai) and there are also other things like spaceships. (Similar to the Amanto in Gintama) So basically, if you enjoyef watching Himawari!!, I'm sure that you'll love Gintama.