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.
Crying could be described according to different situations and characters. There were a few possible ways to describe it:
1. Crying sadly: The eyes are red and swollen, and the tears are constantly flowing. The lips are slightly opened, as if they are silently pouring out the pain in their hearts.
2. Crying in despair: Tears poured out like a waterfall. His eyes were hazy and he looked depressed as if he had lost all his strength.
3. Crying angrily: The eyes are red and swollen, and the tears are like boiling flames. The expression on the face also becomes angry and resentful.
4. Crying in surprise: Tears instantly gushed out of her eyes as if expressing her inner ecstasy and gratitude.
5. Crying in fear: Tears flow from the eyes. The trembling body and helpless heart make people feel fear and uneasiness in their hearts.
Different crying forms could show the character's inner emotions and personality characteristics, and at the same time, it could allow the reader to better understand the character's psychological state.
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.