Fairy Tail and Naruto are both popular shonen franchises with classic shonen protagonists, and these series are also known for their highly diverse magic systems. Many wizards and ninjas fight hand to hand or with elemental magic, but it's also an option to summon some extra help. The summoning systems of both series are loosely similar: celestial magic, and kuchiyose summoning jutsu.
In Fairy Tail, Lucy Heartfilia is a noted celestial wizard, and she is working hard to collect all the gold keys and silver keys so she can summon all kinds of spirits to aid her in battle. Meanwhile, characters such as Naruto Uzumaki, Danzo the Hokage, Jiraiya the toad sage and even the rogue Sasuke Uchiha make good use of summoning jutsu in a fight. How do these systems compare?
Celestial Magic: Summon The Western Zodiac
There are exactly twelve gold keys, one for each sign of the astrological system, from Pisces to Leo to Scorpio and beyond. These spirits vary widely in their personality, appearance and abilities, with Gemini being able to clone an enemy while Leo (Loke) is a powerful melee fighter and Scorpio can create devastating sand attacks. And Sagittarius, true to its original sign, can fire flaming arrows from his bow. On top of that, the celestial magic system supports a variety of silver keys, which summon lesser spirits such as Horologium and Pluie. In a fight, the celestial wizard must hold up a key and verbally announce the spirit's name, and the spirit will appear right next to the summoner (remote summoning isn't possible). Most celestial wizards only have the strength to control one spirit at a time, but strong wizards, if pushed, can summon two at once, which Lucy sometimes did. Yukino, a wizard belonging to the Sabertooth guild, could easily switch between Libra and Pisces during the Grand Magic Games tournament arc.
A celestial wizard must get his or her hands on a key and make a formal contract with the spirit, and that spirit is utterly bound to the summoner's will. A minor exception is Loke, who has summoned himself more than once when Lucy was in trouble during a fight. These contracts will end after the summoner's death, and a key may take on a new master right away. If a gold key is broken on purpose, then the Spirit King himself will be summoned forth, a titanic spirit with boundless power. Only rarely is this done, however.
Summoning Jutsu: The Dogs Of War
In the world of Naruto, the summoning system is known as kuchiyose summoning, and it is based on contract scrolls, rather than keys. A ninja may sign his or her name onto a contract scroll and offer a print of all five fingertips (using their blood as ink) to formalize the contract. Now, the ninja can place their hand directly onto the ground and declare the summoning jutsu verbally, and any ninja animal bound to that scroll will be brought forth in a burst of smoke. How powerful will that animal be? The animal's strength will match however much chakra the summoning ninja used for that instance of the kuchiyose summoning jutsu, meaning this jutsu can greatly reward powerful ninjas who can offer a lot of chakra at once. For example, there are many toads bound to a certain scroll, and a weaker ninja (such as a genin) will summon a small toad warrior. Someone much stronger, such as Jiraiya or Naruto in Sage Mode, might summon the great Gamabunta himself, a mammoth toad who rivals the nine-tailed fox in size (and possibly strength).
The ninja animals and their summoners are not exclusive to one another, like the celestial keys of Fairy Tail are; a certain toad may be summoned by any number of people who have the same contract. And in the Naruto series, other animals have appeared too, such as when Orochimaru summons Manda the snake, when Sasuke summons a hawk, or when Kakashi Hatake summons a whole pack of loyal ninja dogs. In fact, two ninjas can pool their chakra to summon a mighty animal that neither of them could have summoned alone. However, the animals are not automatically loyal to their summoner; in fact, they might even turn on their summoner if they find a good reason to. So, a summoner ninja must use discretion when making a contract and summoning the animals bound to that scroll.
Which Summoning System Is Better?
As a whole, the kuchiyose summoning system is the more practical one, since it is possible for more than one ninja to access the same animals via that contract, and two ninjas can pool their chakra for an extra-powerful summoning. What is more, the summoner ninja only needs to place a hand on the ground and offer chakra to summon some animals, while a celestial wizard must have their key on hand. If their key is lost or the wizard can't touch it for some reason, they are practically powerless, while Naruto ninjas don't have that problem. It's even been shown that if a ninja should die and they are revived, such as the Edotensei jutsu, they can still access their summoning contracts.
Celestial magic does have one advantage: the option to summon the mighty Spirit King in emergencies, even without having magical power to match. By contrast, summoning Gamabunta takes a lot of chakra.