Ado is a female vocalist born on October 24, 2002, in Tokyo, Japan. Although her music has been listened to and her videos watched millions of times, she does not reveal her face or real name, choosing to use anime-style videos and illustrations - even in interviews.

In 2014, Ado took an interest in music after a software of the video-sharing website Niconico was released on Nintendo 3DS. She began watching videos on the small screen of Nintendo 3DS, and was impressed by the cover singers on Niconico, who sang without showing their faces.

Years later in 2017, Ado began singing as an utaite (an internet cover singer) on Niconico, after uploading a video of herself singing a cover of Kimi no taion on January 10, 2017. On Nippon TV she said that during the time she was an utaite singer, she covered her closet in soundproofing material that she bought online and recorded in it.

In 2019, she featured in Kujira's digital single Kinmokusei, which was released on December 23, 2019. A couple months later, she featured as a vocalist in a digital single Shikabanēze by jon-YAKITORY, which was released on March 29, 2020. In May 2020, she participated in Pony Canyon's compilation album PALETTE4. She released two songs, Call boy by syudou and Taema naku ai-iro by Shishi Shishi, as digital releases.

On October 15, 2020, Ado announced that she would make her debut with Universal Music. On October 23, the day before her 18th birthday, she released the digital single Usseewa written by vocaloid producer syudou. The music video, released on her own YouTube channel, reached 5 million views by November 14. On December 10, 2020, Usseewa ranked number 1 on Spotify Viral 50 Japan. On December 24, she released her second single Readymade written by vocaloid producer Surii, as a digital release.

By January 23, 2021, Usseewa had reached 40 million views on YouTube, and on February 3, 2021, it ranked number 1 on both Oricon Digital Singles Chart and Oricon Streaming Chart. On February 14, she released her third single, Gira Gira, written by vocaloid producer teniwoha, as a digital release. Four days later on February 18, the number of subscribers on her YouTube channel exceeded 1 million.

On March 15, 2021, Usseewa reached number one on the Billboard Japan Hot 100, and on March 20, the music video on YouTube reached 100 million views, 148 days after its release. On March 29, Usseewa reached 100 million plays on the Billboard JAPAN chart “Streaming Songs” after 17 weeks from charting-in, which was the sixth fastest in history and the youngest for a solo singer.