Well, there are different ways it can happen in fanfiction. One way could be that Naruto and Mizuki are in a battle, and during the fight, Naruto accidentally activates a latent ability that allows him to absorb Mizuki. Maybe there is some sort of ancient seal on Naruto that reacts to Mizuki's presence and starts the absorption process. Another possibility is that Naruto is exposed to a strange chakra - infused object that was once connected to Mizuki, and this object triggers the absorption.
In fanfiction, Naruto might absorb Mizuki through a magical or mystical encounter. For instance, they could be in a special place, like an ancient temple, and there is some sort of energy field there. When Mizuki attacks Naruto in this place, the energy field somehow causes Naruto to absorb Mizuki instead of being harmed. Or perhaps there is a powerful ninja who wants to experiment on them and uses a forbidden technique that results in Naruto absorbing Mizuki.
In this kind of fanfiction, Mizuki might save Naruto from a dangerous enemy attack. Maybe he uses his own skills to fight off the attackers who are about to harm Naruto.
In some Naruto fanfictions, Naruto might absorb DNA through special jutsu or abilities. For example, he could have a unique kekkei genkai that allows him to take in and assimilate the genetic material of others. This could potentially give him new powers or abilities related to the DNA he absorbs, like if he absorbs the DNA of a Sharingan user, he might gain some form of Sharingan - like abilities.
In some Naruto fanfictions, Naruto might absorb animals through special jutsus or abilities. For example, he could have a unique kekkei genkai that allows him to take in the essence or chakra of animals. It could also be related to some sort of pact or bond he forms with the animals, which then enables him to absorb their powers.
In some fanfictions, it could be through a special jutsu. Maybe Naruto discovers a long - forgotten jutsu that allows him to merge with his dark counterpart. This jutsu might require a great deal of chakra control and concentration.
There are fanfictions where Naruto absorbs the bijuu during a life - threatening battle. As he is on the verge of defeat, he somehow taps into an unknown power within himself and ends up absorbing the bijuu to turn the tables. This often involves a strong emotional connection and a will to protect, which acts as a catalyst for this absorption.
In some fanfictions, Naruto might absorb chakra through unique jutsu. For example, he could have a new, self - created technique that allows him to draw in ambient chakra from nature more efficiently than in the original series. This could be a result of some special training he undergoes in the fan - created story.
In some fanfictions, Naruto might absorb Chakra through a special jutsu. For instance, he could use a self - created jutsu that allows him to draw in Chakra from his surroundings or from other characters he's in contact with.
In some fanfictions, Naruto might absorb souls through a special jutsu or power that is unique to that fictional storyline. It could be something he discovers during a dangerous mission or as a result of some strange encounter. For example, he might inherit a power from an ancient ninja clan that allows him to absorb the souls of his enemies, which he then uses to gain strength or knowledge.
In some fanfictions, Naruto might absorb Momoshiki through a unique kekkei genkai. For example, if the author creates a new form of chakra manipulation that allows Naruto to assimilate Momoshiki's power during their battle. This could be a result of Naruto's Uzumaki bloodline having some hidden potential that gets unlocked in the heat of the fight.
In some fanfics, Naruto absorbs the bloodline through a special jutsu. For example, he might find an ancient scroll that contains a jutsu allowing him to transfer and absorb the genetic traits related to a bloodline.