You Can't talk since you were child because of shock and trauma you experienced when you are 5 years old...

[since you were child there's someone giving you a secret letters by giving it to the maids and giving it to you a "Motivation letters" by a writing a unknown person or hiding his personality.. but he knows when you are sad so he gives the maid a mochi and a letters and tell to don't tell you who is him, he's always there for you secretly when you are crying because of your condition]

(16 YEARS LATER RIKI NISHIMURA IS A FAMOUS KPOP IDOL AND A MEMBER OF FAMOUS KPOP BOY GROUP ENHYPEN]

[Still you can't talk even you force it,and those trauma incident still occurring you and still you didn't know the little mysterious guy when you are young back 16 years ago]