It could be a genetic mutation in the fanfic's storyline. Some strange event or factor could have caused a change in Bardock's genes, making it possible for him to become Super Saiyan. This genetic change might be related to some ancient Saiyan lore or a new element introduced in the fanfic's universe.
The relationship could develop in a more emotional way. Maybe Trunks gets injured badly in a fight, and Vegeta realizes how much he cares for his son. He then becomes more protective and affectionate towards Trunks. On the other hand, Trunks could also start to understand his father better, seeing that Vegeta's tough love is actually a way of showing his love and concern. This new understanding could lead to a more harmonious and loving relationship between them.
Another plot could be that a mysterious entity bestows the power of Super Saiyan Blue on Naruto. He then has to keep it a secret from his friends and village while also using it to protect them from a new and powerful enemy. This would create a lot of internal conflict for Naruto as he tries to balance secrecy and heroism.
One great Super Saiyan Blue Goku crossover fanfiction is 'Goku in the DC Universe'. It's really exciting to see Goku interact with Superman and other DC heroes. He has to adjust to the different power levels and rules in that universe.
Sure does. Goku attains the perfected SSJB in the manga during intense battles and as part of his power-up journey. It's a significant moment for his character development.
One possible analysis could be that it might explore the complex relationship between Vegeta and Trunks. Maybe in this fanfiction, Vegeta's strict training methods could be seen as 'hurting' Trunks in a sense, like pushing him too hard physically or emotionally. It could also delve into how Trunks copes with that and if it ultimately makes him stronger.