Rubbish protagonist, I can do it too!

"Makoto Ito, not smooth enough." "Sakura Manji, too chuuni." "Shinji Matou, too ordinary." "Zig, useless."
"One thing I learned from my short audience career is that the more works I watch, the more I will discover the incompetence of the protagonist!"
"what do you want to say in the end!?"
"Trash protagonist, I can do it too!"
"Okay, you can do it."
"???"
Since then, the world has lost a keyboard man, and has gained a traveler who travels through different worlds.
"Fuck (Chinese-Japanese bilingual), let a seven-year-old child participate in the Holy Grail War, you are a fucking genius!" Only six years old, a harmless kelp with black lines all over his face.
Before he finished complaining, his father led a timid little girl over and introduced, "Shenji, from today onwards, she will be your younger sister, her name is Sakura, Matou Sakura."