K.K. Birthday

"K.K. Birthday" is a K.K. Slider song that first appeared in and later reappeared in. It is considered a secret song, as it can only be obtained during a K.K. Slider performance on the player's birthday (or the Saturday before prior to ). It is not obtainable in, but it is performed by K.K. Slider. None of the villagers own this song, although it will play in a villager's house on the day of their birthday; if the villager already had a stereo with a song playing, it will be replaced by this song. In, it is one of five songs that cannot be reordered via Nook Shopping once obtained; the other four are "Animal City," "Drivin'," "Farewell," and "Welcome Horizons."

The song's composition and melody is based heavily on the traditional "" song, which was not in public domain at the time of 's release. However, it is much longer in comparison to its source material, with a more intricate structure and harmony.

Album cover
The album cover for "K.K. Birthday" features a birthday cake decorated with white icing, strawberries, green lit candles, and icing toppers in the shape of Tangy holding a birthday present and K.K. Slider playing a guitar. An edible cookie at the center of the top of the cake reads "Happy," and text at the bottom of the album cover reads "Birthday." In, the word "Birthday" is blue and in a horizontal format, while in , the word is red and curved upward.

In
In, K.K. will perform "K.K. Birthday" on the closest Saturday prior to the player's birthday (or the actual day, if it naturally falls on a Saturday). There is no aircheck of this song.

In and
Although "K.K. Birthday" is not present as one of K.K. Slider's songs in and, a unique instrumental arrangement of the song plays as background music when the player is first greeted by another villager upon starting the game on their birthday.

In
In, "K.K. Birthday" can be played in villagers' houses during their birthday. It also plays in the house of the villager that invites the player during their birthday. K.K. will perform this song on the Saturday near the player's birthday. Unlike, K.K. gives an aircheck of this song. If the player's birthday is not on a Saturday, K.K. will also play a DJ remix on that day in Club LOL. (This is referenced in DJ K.K.'s trophy description in .)

In
In, "K.K. Birthday" can be played in villager's house during their birthday. It also plays in the house of the villager that invites the player during their birthday. K.K. will also visit the island solely to perform this song on the player's birthday regardless of the day of the week, after which he will give the player the aircheck.

In
In, "K.K. Birthday" is played in the houses of Bunnie, Jingle, Melba, and Zipper.

In other media
A sheet music book released in Japan by Yamaha titled "みんなで楽しむ あつまれ どうぶつの森(ステッカー付)" featured piano solo sheet music for "K.K. Birthday."