Who could be the second bijuu that Naruto gets in the 'naruto has two bijuu fanfiction'?

Well, having two bijuu would likely make Naruto extremely powerful. He could potentially combine their unique chakra natures and abilities in combat. For example, if one bijuu has a fire - based ability and the other has a water - based one, he might be able to create new and unexpected jutsu by mixing them. Also, it would change his standing in the ninja world. People would probably be more in awe or more fearful of him, depending on their stance towards Naruto.

It could be an ancient sage. In Naruto lore, there are sages who have had a great influence on the world. An ancient sage could be the one who created or fathered the bijuu. Maybe he had some great power and knowledge that allowed him to bring the bijuu into existence.

In many Naruto fanfictions, if Naruto has three bijuu, they could be the Nine - Tails (Kurama) which he already has in the original series, perhaps the Eight - Tails (Gyuki) as it has a connection with Naruto's world and Akatsuki's hunt for the bijuu. And another could be the Three - Tails (Isobu). However, it really depends on the specific plot and creative direction of the fanfiction.

The Akatsuki might also be the main antagonists. They were after the bijuu in the original story. With Naruto having two, they would surely target him. They might see it as an opportunity to gain an even greater edge in their plan to control the world.

In some fanfictions, this might happen when Naruto faces a particularly powerful enemy and needs an extra boost.

In fanfiction, if Naruto is half - bijuu, it could mean he has enhanced physical abilities. For example, he might have greater strength and speed like a full - bijuu. His chakra reserves could also be much larger, allowing him to perform more powerful jutsu for longer periods.

One possible plotline could be Naruto struggling to come to terms with his half - bijuu nature while also dealing with his relationship with the fem bijuu. Maybe there are other characters who are either afraid or in awe of his unique state, leading to various conflicts.

His power becomes extremely overwhelming. With all nine bijuu, Naruto gains access to an insane amount of chakra. He can perform massive jutsu without much strain. For example, his Rasengan could potentially be magnified to a scale that could destroy large areas with ease. Also, his physical abilities like strength and speed would be enhanced to superhuman levels due to the boost from the bijuu's power.

If Naruto has all bijuu in fanfiction, it's a huge game - changer. Firstly, his training and growth would be on a whole new level. He'd have to learn to balance the different natures and personalities of each bijuu. His opponents would have to come up with new strategies to face him. Moreover, it could open up stories about how he uses the bijuu to bring peace to the ninja world. Maybe he could use their power to stop wars and conflicts, or to protect the weak. It could also lead to interesting interactions with characters like Sasuke, as they might have different views on how to use such great power.

Well, one possible storyline could be that Naruto has to learn to control the power of the two bijuu simultaneously. He might face challenges in balancing their different natures and abilities.