Guts is purely fictional. It's a concept or character that exists within the realm of imagination and creative storytelling rather than being based on reality.
Perhaps in this fanfic, Griffith has turned into something truly evil and a threat to the world Guts cares about. Guts, being the warrior he is, might feel it's his duty to put an end to Griffith to save others. Also, Guts could be driven by his own sense of justice. If Griffith has wronged innocent people, Guts may decide that killing him is the only way to set things right.
It depends on the specific fanfic. Some fanfics might have Guts killing Griffith as a major plot point, while others could take a different direction and not have that happen at all.
Game editing was one of the most important ways to showcase the charm and skills of a game. To edit a game video, you could use the game bar that came with the Windows operating system to record and edit the game video. When playing a game, press the Windows logo key +G on the keyboard to open the game bar. From the capture component in the game bar, choose "Start recording now" to start recording the clip, and choose "Stop recording" to end the recording. If it's a full-screen computer game, you can start and stop recording using the Windows logo key +Alt+G. When editing a game video, there were some techniques that could be used to improve the quality of the video, such as determining the theme and style of the editing, choosing the most exciting material, and controlling the rhythm of the video. As for the specific editing software recommendation, it was impossible to know based on the information provided.