The Ōtsutsuki clan is by far the strongest clan introduced throughout the Naruto franchise. They regularly use the power of the Ten-Tails and the Divine Tree’s Chakra Fruit to amass power for themselves. When these great powers were formally introduced to the series, they could only be described as immeasurable. However, something about this description has changed with time. It still applies, but its meaning has spread to encompass more characters.
Going into Boruto: Naruto Next Generations, several more members of the Ōtsutsuki clan have been introduced. While they're certainly strong, there has to be some way of determining who the strongest is. While nothing is stated outright, several lines of dialogue and actions performed are available to suggest how the Ōtsutsuki rank among one another. With that said, here are some of the strongest Ōtsutsuki in shinobi history, where their power comes from, and which one of them could be called the strongest.
The Godlike Kaguya Was Virtually Unstoppable
Kaguya was undoubtedly the strongest character introduced in the original Naruto series. She acquired her godlike power by eating the Chakra Fruit of Earth's Divine Tree. That chakra was disseminated among her children, as well as their descendants and the people who would go on to become shinobi. She makes it her sole purpose to retrieve her dispersed chakra and make the Divine Tree bear another Chakra Fruit.
When she was introduced to Naruto proper, she was nigh unstoppable. It took the combined efforts of the original Team 7, Obito, and the spirit of her son Hagoromo just to seal her. As the Mother of Chakra, her theoretical best would be more powerful than any ninja on Earth could ever be.
Momoshiki's Ultimate Form Required Naruto & Sasuke to Defeat
Momoshiki was introduced in Boruto as the real reason Kaguya wanted so much power. According to Sasuke, Kaguya might have been trying to amass power and cultivate a White Zetsu army to fight off potential invaders from the Ōtsutsuki clan. This implies that, for how powerful she was, she was worried about her odds if she ever had to go up against her own kind.
Momoshiki was fairly powerful at first, but he was able to develop himself even further by consuming his partner Kinshiki. His resulting new form required the combined efforts of Naruto and Sasuke to beat; it's never stated directly, but many fans believe these two have grown strong enough to fight Kaguya. He was eventually finished off with a well-placed Parent and Child Rasengan. The way he's built up makes him sound powerful, but his on-screen performance leaves his true potential nebulous.
Isshiki Was a Formidable Foe, Despite His Disadvantages
Unlike the other Ōtsutsuki, Isshiki's powers are actually severely limited. He arrived on Earth along with the lower-ranked Kaguya; the plan was to sacrifice her to the Divine Tree and eat the resulting Chakra Fruit, but Kaguya turned on him and left him for dead. Isshiki survived by taking over the monk Jigen, whose body lasted him all the way into the time of Boruto. However, by this time, Jigen's body was on the verge of decay and Isshiki needed to transfer into a new host via Kāma.
Despite all of his disadvantages, Isshiki was still the strongest Ōtsutsuki yet. He was able to beat Naruto and Sasuke in a two-on-one fight. The goal for beating him became stalling him out until his body died, which required Naruto to sacrifice Kurama. It’s frightening to think what Isshiki would be like in top condition.
Final Verdict: Who Was the Strongest?
Among these top-tier Ōtsutsuki, Isshiki is probably the strongest one that Naruto, Boruto, and their friends have ever had to face. Momoshiki was tough but manageable. Kaguya might have been unbeatable at her best, but there’s no way of knowing that without rendering every other chakra user on Earth helpless. Isshiki was able to make even the adult versions of history’s strongest ninja fall before him. In any case, these celestial beings make it clear that the Ōtsutsuki clan is not to be trifled with.