It was him who made Korone like that.
She used to be an ordinary Japanese school girl laughing and hanging out with bunch of her friends.
But the boy next door changed it all. He ruined Korone's life.
He was so introverted and alienated in school, and suffering from severe bullying. Korone was the only one saying hi and talking to him in school as they have known each other since they were born. But his constant blaming and throwing harsh words towards her made her insane. She lost her sanity and became a shut-in, and came to play video games for literally 24/7. He realized what he had done, repented, and determined to atone for the wrong by always staying with her.
Now all his hairs and teeth, and some of his eyeballs and testicles were pulled out. He lost some of fingers as well and his scrotum was torn up. And what viewers haven't realized is his knees also shuttered. Those were what Korone have done when she became uncontrollable and what he accepted with smile.
He believes someday Korone may become her old self again, and that'll be the day when she puts a period on her streams.
