The singer's name is Ado. She debuted with that song "Useewa" when she was 17 years old. She is now known as Japan's #1 singer. She is 21 years old now and is currently on a concert tour around the world. She'll be in the U.S. pretty soon. I would definitely recommend taking a listen to more of her songs. Her range is absolutely crazy. Some of my favorites are Odo, Show, Unravel (which is a cover; I would recommend the live version), and Aishite Aishite Aishite (which is another cover of a vocaloid track that was said to be almost impossible to sing). I would definitely recommend going down the Ado rabbit hole. Her singing is transcendent!
I get it. This is a reaction channel. Akane has so so so many vids in her channel, maybe they could have studied her teaching style and BTS vids a bit.