His body might not be fully adapted to the new bloodline right away. Just like when he first started using the Nine - Tails' chakra, there could be side effects. His chakra control could be thrown off, or he could experience physical pain when trying to use the new bloodline - related abilities until he fully masters it.
The new bloodline ability might not be accepted by the village. Some in the Hidden Leaf might see it as an unnatural or dangerous development. This could lead to distrust and even potential conflict within the village, as some might fear Naruto has become too powerful or has strayed from the traditional ninja ways.
Well, the main drawback is the damage to his body. The Eight Gates technique is very taxing on the body. Naruto could end up with permanent damage if he uses it too often. Also, it might change his personality. The intense power of the Eight Gates might make him more aggressive, which could be a problem when dealing with his friends and allies. And from a strategic point of view, if he uses it too early in a fight, he could exhaust himself and be vulnerable to counter - attacks.
One drawback could be that it might disrupt the balance of powers in the Naruto world. Naruto was already a powerful ninja, and adding Sans' powers could make him overpowered compared to others, which might make the story less interesting as there would be less of a challenge for him.
One potential drawback could be the moral implications. Controlling someone else's blood is a very invasive and potentially cruel ability. Naruto, who is known for his kind heart, might struggle with using such a power. Also, it might be difficult to control precisely, and he could accidentally harm allies if he's not careful.
The drawbacks could be significant. He may start to isolate himself because he knows things that others don't. This could lead to a breakdown in his relationships. And if the wrong people found out about his ability, they would surely try to use it for their own evil purposes. He would constantly have to be on guard against that. Another issue is that the future he sees might not be set in stone. If he made decisions based on what he saw, but then the future changed, it could lead to chaos.
There could also be a mysterious outsider from another land. They've heard about the power of the Naruto world's bloodlines and come to steal them. This outsider might have their own motives, like using the bloodlines to strengthen their own people back in their homeland. They would be a completely new and unpredictable element in the Naruto universe, making for an interesting story as the characters try to figure out who this unknown thief is and where they come from.
One drawback could be the strain on his body. The Sharingan is a powerful dojutsu, and Naruto's body, which is used to his own chakra system, might not be able to handle it well at first. This could lead to fatigue and over - exertion during battles.
One drawback could be that absorbing too many bloodlines might make it hard for him to control his new powers. He could lose his sense of self or go berserk. Another is that other ninja might see him as a threat and target him more often. This would put him in constant danger.
One potential drawback could be that Naruto might accidentally hurt his friends or allies while using his super - speed. If he's not fully in control, he could run into them or cause a gust of wind that knocks them over. Another issue could be that he might rely too much on his speed and neglect his other ninja skills, like his shadow clones or his ability to sense chakra.
It might also be possible for new characters to be the main characters in this fanfiction. For example, a young ninja who discovers a Keyblade and has to learn how to use it while also dealing with the politics and power struggles in the Naruto universe. They could be from a minor clan but rise to prominence through their Keyblade skills.
There could be copyright infringement. The characters and the basic world settings are usually owned by someone else. Using them to create sex - related content without permission is against the law.