Isuca

As much as I'd like to give you more than a list with similarities and differences, with the setting of Isuca appearing to be a direct copy of Shakugan no Shana's there is very little else to say. As such; both series have monsters from another world who need to suck out humans' lifeforce in order to be able to remain in our world. Fighting those monsters is a young tsundere with a love for the word "Urusai" helped by an everyday schoolboy with a certain mysterious power. Needless to say they end up living together. Saying it's all the same would be a bit unfair though, Isuca focusses more on ecchi/harem, while Shana keeps it at a love triangle with considerable less intrusive echiness and censoring. Furthermore the start of Shakugan no Shana is far superior to the start of Isuca. read more 

Both are a series about Spirit Exorcist, have a harem and have a Niko girl as a main character. 

Both involve the use of magic and the main character fighting spirits/demons. The use of names and knowledge of someone's true name is also apparent in both, but is touched on more in Isuca. Both have comedic moments but can get serious. Tsugumomo is more on the comedy side though. 

Both include ecchi (however moreso in DXD) a harem and demonic powers, battling against monsters. 

Youjuu Toshi (aka Wicked City) is a classic horror hentai about shapechanging monsters from another dimension and the people who hunt them. Isuca, similarly, revolves around a family of specter hunters and the mysterious mc who wanders into the hunt. Specters drain life force and give intense pleasure in return. The specters in Isuca look like they were inspired by Youjuu Toshi's creature artwork. However, Isuca is ecchi not hentai so it isn't as graphic sexually, and doesn't have the prolonged monster rape scenes of Youjuu Toshi. Still, it is a nice bit of erotic horror.  

Both are very ecchi anime with lots of kisses/borderline porn moments, both are about people who need to kiss to trigger their power to fight opponents. Valkyrie Drive Mermaid is a shoujo ai while Isuca is straight.  

Gore and boobs to further stain the soul of the avid degenerate anime fan. Both animes animated by Arms, they share the same kind of dark ambience worsened by lots of blood and mutilations, and somewhat lightened by a rather ludicrous amount of ecchi scenes. 

It has a similar style in the sence that the main male character is supplying the female protagonist with some sort of life force or energy. Also the romantic relation between the two characters changes from initial hate to final love like relation in both series. 

Both are ecchi series with a plot revolving around protecting humans from spirits and the supernatural. In both, one MC is a powerful exorcist and another MC is has an abundance of spiritual energy that they use to support their partner is exorcising yokai. Ayakashi Triangle leans a bit more comedy, while Isuca is a tad more serious, but that does not get in the way of classic ecchi shenanigans that are abundant in both series. 

similarities: male character have some special powers both of the story deals on spirit matters girls needed the boy because of his special power 

Similarities: 1. Both almost have the same genre. 2. Both plots involve dealing with the supernatural. 3. Both Main Girl character's who were suppose to be the guy's mistress found themselves being the servant due to some setbacks. 4. Both Main girl characters were powerful and tsundere. 5. Both Main Guy characters have special ability. Dissimilarities: 1. When it comes to the Main Girl's attitude one was a certify tsundere while the other was a bit defensive but accumulating. 2. The Main guy character in one anime can kick ass, while the other guy from another anime....well let's just say he a bit of a wuss. 3. The level of fanservice of one anime is more brazen than the other. 4. When it comes to romance, one anime has a more serious tone than the other.  read more 

they seem very similaur main character sharing power to power up another character but reveresed in campione the guy gets the power up. 

A heroine with mysterious powers, armed with a bow and arrow. Together with a boy of unknown origins, they fight supernatural creatures not of this world, with the occasional help of a party of humans and the very supernatural beings they aim to either befriend, or exorcize.  

Both series are quite similar because the main character is involved in eliminating dark spirits from the world. And both series are quite comedic except that isuca has some fan-service. Besides, both main characters have a boy assistant that kinda love each other.