One possible plotline could be that Broly, in his rage, accidentally provokes Beerus. Broly, not knowing who Beerus is, attacks him. Beerus, initially amused, decides to teach Broly a lesson but soon realizes that Broly's power is growing at an alarming rate. This leads to an intense battle where Broly pushes Beerus to use his full power. Another plotline could be that Beerus hears about Broly's power and decides to test him. He travels to Broly's location and challenges him. Broly, seeing Beerus as a threat to his friends or his planet, fights back with all his might.
One possible plotline could be that Cell, seeking to prove his superiority, challenges Broly. Broly, in his usual berserk state, accepts without hesitation. The fight could start with Cell trying out his various attacks like the Kamehameha - like Solar Flare and his physical strikes. But Broly's power is just too much and he starts to overpower Cell. However, Cell then reveals a new, hidden ability that he has been developing in secret and the tables are turned for a while.
A plotline could involve Broly being sent to Kale's universe by some sort of interdimensional rift. Kale initially sees him as a threat and attacks. But as the fight progresses, they start to understand each other's power and motives. Or perhaps a fanfic could have a story where both Broly and Kale are training on the same planet. Their training methods clash, leading to a fight where they both learn from each other and grow stronger in the process.
A plotline could start with Frieza hearing about Broly's power and being jealous. He then devises a plan to ambush Broly. But Broly, being extremely perceptive in his own way, senses Frieza's approach and is ready for the fight. As the fight progresses, Frieza realizes that Broly is much stronger than he expected and has to use all his dirty tricks to try and win. Or perhaps the plotline could involve Broly being captured by Frieza's forces, and then Broly breaks free and goes on a rampage against Frieza and his minions.
Well, in some fanfictions, the battle might start as a misunderstanding. Spiderman could be in Gotham chasing a bad guy who has a connection to New York and Batman mistakes him for a new threat. In this case, Spiderman would try to explain himself but Batman, being the brooding detective, might not listen. Then there are scenarios where the battle takes place in a neutral location like an abandoned warehouse. Here, both of them have to rely on their skills and resources. Spiderman would use his webs to create obstacles and Batman would use his gadgets to break through them. Also, there could be a scenario where they team up against a greater threat first and then due to a clash of egos, they end up fighting each other.
In a 'Naruto vs Ichigo' death battle fanfic, there are several important factors. Naruto's chakra control and his ability to learn new jutsu quickly are important. He can also use nature transformation, which can give him an edge against different opponents. Ichigo's spiritual pressure is a major factor. The more he can control and increase it, the more powerful he becomes. Also, his ability to sense and react to his opponent's attacks is crucial. Another factor is their experience in battle. Both have faced many tough opponents in their series, and that experience will play a role in how they fight each other.
Well, it's really hard to say for sure. Naruto has his amazing ninjutsu and the power of the Nine - Tails. Ichigo, on the other hand, has his Soul Reaper powers. But if I had to pick, I'd say Ichigo. His Bankai and Hollow powers give him a huge edge in terms of raw power and speed.
In the 'naruto vs ichigo death battle reaction fanfiction', reactions can be quite diverse. For Naruto fans, they might cheer when he uses his Rasengan in a creative way against Ichigo. Ichigo fans, on the other hand, would likely react strongly when he unsheathes his Zanpakuto and shows off its special abilities. There could also be a sense of disappointment from fans if their favorite character is losing or not performing as expected.
One common plot twist is when the powers of Naruto and Ichigo somehow merge during the battle, creating a whole new set of abilities that neither of them expected. This can change the entire dynamic of the fight.
You can try platforms like FanFiction.net or Archive of Our Own. They usually have a wide variety of fanfictions including those related to 'Naruto vs Ichigo' Death Battle.