Konjiki no Gash Bell!!

Both protagonists in the series receive a demonic child which they have to use to defend their lives from people and other beings in order to achieve a certain goal. Gash is focused more the action and adventure genre while Beelzebub is a pure episodic comedy manga with several action-themed plots. 

Both of these are fighting anime. But they share a similar since of humor, and animation style. Ueki - is a battle anime where the winner's "god candidate" (or coach) becomes god. Zatch Bell - is a battle anime where the winner's doll becomes king. 

Both are involved with tournament-survival game, where book owners (Gash Bell)/diary's owners (Mirai Nikki) will have to destroy each other book/diary. The winner, which is the last one standing will became king (Gash Bell)/god (Mirai Nikki). Mirai Nikki is darker than Gash Bell in many prospects including destroying diary will lead to death of the owner, thus owners mostly wouldn't care less to kill each other directly. While in Gash Bell, the demon of the book will return to demon world after destroying the book.  

In Rozen Maiden there are 7 dolls and each one must fight against each in a battle called the Alice Game. Each one is partnered up with a human so they can use the human for energy, like in Zatch Bell they use the power of the heart. They call the human Mediums, and Mediums are basically like the Book Owners. They collect each ones Rosa Mystica and the last one standing becomes Alice and is loved and cared for by Rozen (the guy who made the dolls). In Zatch Bell they each fight one other and the burn the books of each other and the Last one becomes King of the Demon World. read more 

Very similar shounen for their silly humour and cartoonish style, with exaggerated facial expressions, foolish/loud large-mouthed characters, ever-present action and friendship themes. 

Same theme, Sekirei is just a pervier version of Gash Bell, lol. 

Both series deal with protagonists who receive a supernatural kind of power. One can talk with spirits and makes one his partner, while the other gets a demonic child as his partner. A competition starts as they have to fight for their lives and to claim a title of "Shaman King" and "Demon King". Both feature a lot of fights and a series of small adventures.  

Strange, but hear me out.... Both very action heavy with over the top moments Character very colourful with a diverse cast Premises in terms character motivations are similar Animation a spectacle to behold ...Plus both share a canny explosive feeling of passion. XD 

Fullmetal Alchemist: Brotherhood provides a really strong and solid history with memorable characters, unbelievable plot twists and amazing fights. While Konjiki no Gash Bell can't compete at his max with FMA:B, I found Kiyomaro and Gash's story to be pretty similar to Ed and Al's one. While in FMA:B, the brothers have to find a Philosophal Stone, Kiyomaro has sworn to make Gash the Mamodo King. Everything decorated with amazing arcs, incredible fights and, in the end, similar values. 

Stoic men meet and have to take care of kids with weird powers from another world. The tone is also very similar, and both Gash and Hina love to eat weird fish. 

Gash Bell and Fate have the same system of servants and also both have a protagonist that dont have so much skills but is developing with the time, and both have the similarity of a war of servants... 

I feel they both share a similar premise & overall atmosphere: Humans and monsters partner up together in order to compete at a tournament to achieve a common goal in exchange for greater power that is promised to anyone who emerges victor — which each individual team intends to use either for the greater good or for their own benefit. This makes for a very colorful cast (consisting mostly of kids) in each of these series, featuring unique systems customary within the monster-taming genre that each of their worlds work on, and an array of situations that vary from lighthearted and comedic to unexpectedly serious and at times dark in an "I can't believe they'd show this in a kid's show!?" kinda way; all while remaining consistently earnest in their execution. Really charming, highly creative, and fun experiences! They both also happen to share the fact that they're SUPER underrated and definitely worth giving a try, too!✨ read more 

In both animes, the characters use their power/magic through spells written in their books and they unlock new spell as their characters develop. 

Epic battles with masters and magical servants are basically what builds the background for both series. The characters are summoned from another world/time to fight in a war until the last one standing in order to achieve some goal.  

Middle school student Tsuna has always gone through life in last place; but when he learns that he is getting a tutor to help him raise his game, he had no idea that his benefactor would turn out to be... an infant and a mafia hitman?! As if things can’t get much stranger, Tsuna then discovers that the powerful Vongola family has chosen him to be its next successor – a position that has control over all mafia families. Joined by friends Tsuna unwillingly starts out on his path to becoming a mafia boss – if he can survive the training! 

Seven kids are enjoying their summer when suddenly, a digivice appeared before them, and the next thing they know, they are in the "Digiworld." There, they meet creatures known as digimon. There are evil digimon in the Digiworld, but they are not bad in nature; rather, most of them have been turned evil by nefarious forces. Each child had a digimon waiting for them in the Digiworld; and though not all Digimon are strong, the digivice that the seven kids carry has the ability to allow their Digimon partner to evolve into a stronger type. Together, they will going to embark on a journey to save the Digiworld from pure evil and darkness! read more 

Magic is used in battle in both series. Also each person/monster/demon has different kinds of magic so there's lots of variaty. In both series comedie is mixed in fillers or the battle themself 

both of these anime's are Shounen and there both somewhat magical they both have a lot of friendship speeches but the similarity between the two is mostly based on the fact that there both about a game to win back peace :D there both verry good anime's and i suggest watching them both :)  

Both of them including very good action and advanture. nI both of the series the main characters are in pairs, when someone is the "master" how telling the other one what to do or fighting with the other one, while the other is attacking or turning into a weapon. Both of them really recommended and I gave to both of them 9+ (10 to SoulEater XD) 

Male protagonists are highly intelligent in both of these series plus the voice of Takamine Kiyomaro is also the same voice of Kururugi Suzaku. 

In both animes the characters control some type of demon (in Gash Bell) or dragons (in Dragon Drive) to defeat evil. 

Basically in the beginning of both shows the protaginist was a bit of a wimp for his smarts and felt that people who bullied him were inferior to him.Then one day all that changes when they meet an unwanted partner who somehow gives them the courage and strength to fight back and learn what it means to stand up for yourself, and they slowly forge a bond with their partner that cannot be broken. Also both of them are pretty hilarious. :D 

Both of these are fighting anime Both are involved with tournament-survival game both of these anime's are Shounen both have supernatural fight humans and demons  

Humans control dolls to battle other people. 

Both have humans using their dolls (Machine-Doll) and demon (Gash Bell) to fight different kinds of enemies. In Gash Bell, they want to become the best and obtain the master title, while in Machine-Doll, the main character wants revenge.