15 [Similar Anime] Like Blade Dance of the Elementalers

Strong male character enters a magic-like school and starts his own harem. Both guys enter under extremely unique conditions (Kamito, only male elementaler; Saito, only human boy familliar)
The main love intrest for both boys is a tsundere girl who is consider a trouble student around the school and she treats the other like a slave or servant because of a contract they entered into.
Both our protagonists have a special sword that is conseidered legendary. Their sword interacts with them (Kamito's has an actual human form. )
The main plots of the two go in two different directions but the main premisis and foudantion of the two are very simillar.

Okay, these two animes are really similar just by watching the first episodes.

Seirei Tsukai no Blade Dance:
-Protagonist is the only male in the world that has the power to create a contract with spirits
-Protagonist is forced into an all girls school
-Harem
-Premodern setting in a magical world where shrine priestesses control spirits

Both anime have an only male transferred into an all-girls school setting, with both MC's being able to use an ability which only females can use.

Both series have a MC that is an Overpowered swordsman, yet in his first appearance appears weak. After that he shows power and starts to get a harem of the various girls from his school. The main female is a fire user.

Both take place in a fantasy world where humans make contracts with fantasy creatures; dragons in Seikoku no Dragonar, and spirits in Seirei Tsukai no Blade Dance. In both anime the main character is an boy with special powers, that makes a contract with a very special dragon/spirit; which take the form of a naked loli. Both main characters and their attend a school filled with a lot of beautiful women, of which most are tsundere and there will be a lot of fanservice.

I've always though that these anime feels similar because both are about the main character getting into a school to learn about magic and both of these are harem/ecchi anime.

It is very similar and I'll explain why, both have excellent Light Novels, full of mysteries and the good part are that they are not predictable.
Both anime have the main characters driven by their past, where they got harsh trainament, in kamito case he was an assassin with no emotions at all, until he met Restia, while Raishin had his entire family assassinated by his older brother. Then both met an old around 40 years woman, who gave then more and more trainamente and later a chance to them remake their mistakes, in Kamito's case he became known as Ren Ashbell, the strongest Blade Dancer to date and Raishin got Yaya, the strongest Machine Doll in the world. Then later both join a sort of academy with will allow then to join a tournament and they will meet new companions and create a small Harem of sorts, but both protagonists are not interested in love and always avoid the girls cringe scenes. And lastly both have great story, battles and lastly at all, both are about people who join up with a partner non-human, a spirit in Seirei and a Machine Doll in Machine-Doll and both of the MC partners are smug loli that wants to be their bride and both does not want to get in bed with them. Go to Seirei if you want something fantasy world and a excellent novel to read on Baka-Tsuki, or go to Machine-Doll if you want one in an alternative real world, or see both like I did.

Blade Dance and Bahamut is related in some extent
-Main male protagonist counter the first female protagonist naked in a bathroom setting
-Only boy in the Academy full of girls
-Swords users
-Main female protagonist is always get jealous when the MC interact with other girls
-Two other side female Restia (Blade Dance) and Yoruka (Bahamut) have feeling toward the MC
-Few others main female protagonist are either Elite Knights or Noble rulers of their own family

Both have a pink haired girl with the intention of making the MC her slave;
They're both Romance/Action Anime;
The girl develops love for the boy with time;

At first, I thought that Seiken Tsukai was a sequel to Seirei Tsukai. The mains both look remarkably similar and even the names are easy to confuse but as I watched the first episode of Seiken Tsukai, I realized that it was a entirely different anime. Interestingly though, both anime contain a main who is trying to become stronger and both of them have a harem of women surrounding them. To be honest, I had expected someone to have already recommended these two!

The main character of each series is thought to be some kind of demon king. They also involve going into caves to obtain powers, there's magic, and they're both full of good ole fan service.

main character goes to a High school / only people with powers can attend ......main has irregular power .. romance is based around a loli

Both are action ecchi harem adventure fantasy comedies involving magic and guy dragged in it. Both main heroes encounter violent tsundere pettanko girl that declares main character is her slave.

Both are action ecchi fantasy comedies involving magic and guy dragged in it. Both main heroes encounter violent tsundere pettanko girl that declares main character is her slave. Both main heroes somehow obtain harem of girls.

Similarities:
Both involve characters summoning spirits (servants) to aid them in a fight against other characters. In Seirei it is to win blade dances in F/SN it is to receive the Holy Grail
The summoning marks in F/SN reminded me of the Spirit Seals in Seirei as well as the use of secondary magic
The elemental waffen of Seirei are similar to the noble phantasms of F/SN
The holder of the Holy Grail and the winner of the upcoming blade dance both get a wish granted

COMMON:
In both,the female main characters have pink hair and have some similarities in personality(Moka from Rosario to Vampire has two personalities and one of them is tsundere while Claire Rouge from Seirei Tsukai no Blade Dance is a typical example of tsundere).
In both, the action takes place in a magical world.