The album's musical style is a fusion of genres including pop, dance, rock, reggae and ska.

It became an unprecedented smash hit, selling over 2.29 million copies and remains the best-selling physical single by a female soloist in Japanese music history.

was certified double million by the Recording Industry Association of Japan (RIAJ), her first and last single to receive such a certification.

The album received positive reviews from music critics upon release, calling it more sophisticated than its predecessor.

Concentration 20 was massively successful, premiering at the top of the Oricon Albums Chart with first-week sales of over 824,000 copies.

[9] The title of the album was reportedly chosen because: "the studio at that time was on 20th Street in Santa Monica, and that is where we concentrated".

The album was named so that it could be played with various meanings, such as "people who were 19 years old when Sweet 19 Blues was released are now entering their 20s", and so on, to broaden the imagination.

[10][11] Other well-known artists such as Marc Panther, Koji Kubo, and m.c.A.T (Akio Togashi) also participated in the production of the album.

[9] The album concept was "Fancy & Cool", with the "glamorous and flashy" part emphasized in "Can You Celebrate?"

[11] The album embodies an array of styles including pop, rock and reggae.

[12] Opening the album is the industrial rock influenced track "Concentration 20 (Make You Alright)".

is a power ballad with a gospel-like chorus, a string orchestra and a piano sound.

"A Walk in the Park" was released as the album's lead single on November 27, 1996, four months after the massive success of Sweet 19 Blues.

[37] It also received a double million certification from the Recording Industry Association of Japan (RIAJ) in March 1997, making it her only single to accomplish this.

was released on Christmas Day 1997 to commemorate Amuro's nuptial with Masaharu "Sam" Maruyama and was also successful with about 500,000 units sold, while also being certified platinum in January 1998.

The first commercial was promoting a sun lotion, the second a shampoo, the third a deodorant and the last a moisturizer.

Ted Mills of AllMusic gave the record three and a half stars out of five, saying that the album has "mature effort" written all over it.

[12] Minoru Majin of Amazon praised Concentration 20 as a stronger, simpler, and more sophisticated version of her previous album Sweet 19 Blues.

[52] Concentration 20 debuted at number one on the Oricon Albums Chart, with 824,980 copies sold in its first week of availability.