Definitely. Yakuza 6 serves as the finale for Kiryu's main storyline. However, the Yakuza franchise is known for its rich universe, and there's always a possibility of revisiting his character in some form or another.
Perhaps in the fanfiction, Zero and Kiryu both get cursed by an ancient magic. The curse gives them some of each other's traits while also weakening their own original powers. This forces them to rely on each other more than ever. They go on a quest to find the source of the curse and reverse it. Along the way, they learn about each other's pasts, values, and what really drives them, leading to a deep friendship or respect for one another.
Tappei Nagatsuki is notable for writing 'Re:Zero − Starting Life in Another World'. His writing style is able to convey complex emotions and the development of the story's mystery is really captivating.
Another might be 'Re:Zero − Starting Life in Another World'. It stands out for its unique premise of the protagonist having to relive his experiences in a different world over and over again, leading to a complex and deeply emotional story. The character development is really top - notch.
A common theme is the clash of different worlds. Since it's a crossover, kazuma mikura often has to deal with the differences between his world and the world he crosses into. This can create a lot of interesting storylines.
I think it happens in 'Konosuba: God's Blessing on This Wonderful World!' But the details might vary depending on how you interpret their relationship development.