I haven't come across a Chinese novel that is clearly centered around the phrase 'you have guts'. Chinese novels cover a wide range of themes, from love and family to war and adventure. While courage is a common trait in many novels, there may not be one that is so simply named or themed as 'you have guts'.
There are many novels related to Plants vs Zombies! For example,"The Legend of the Botanic Card Creator","The Botanic Mountain Monarch","The Great Botanic Overlord","Overlord: I Summon Plants vs. Zombies in the Abyss","Where Are the Magical Plants?" Doomsday Plant Lord, Super Plant Zombie System, Family Cultivation: Starting with Plants vs Zombies, I Plant Zombies in the Other World, Playing Plants vs Zombies in the Full-time Mage World, I Cultivate in the Movies, Master Plants, Planting Herbs in the Underworld, and so on. I hope you like this fairy's recommendation. Muah ~😗
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.