There are many groups involved in the production of songs in the industry, but you'll appreciate that writing the title songs is privilegedly admirable. I prepared a selection of title songs whose lyrics were written completely by the members. (Title tracks that are NOT contributed by any other producer or songwriter except members)

12) PLT - IGOHOLIC

Album: IGOHOLIC (2018)

Lyrics: Jin Woo, Gaho, Villain, June, Moti
Composition: Sang Jun, Jin Woo, Gaho, Villain, June, Moti
Arrangement: LONG DRIVE2, Sang Jun, Jin Woo

Not only this song, R&B grup PLT' each song is produced by members.

11) STRAY KIDS - MIROH

Album: Clé 1 : MIROH (2019)
Lyrics: 3racha
Composition: 3racha, Brian Atwood
Arrangement: Brian Atwood, Bang Chan

All the songs of the group come from the 3RACHA, the sub-group consisting of Bang Chan, Changbin and Han.

10) BTOB - I'll be your man

Album: New Men (2016)
Lyrics: Im Hyun-sik, Lee Minhyuk, Peniel, Jung Il-hoon
Composition: Im Hyun-sik, EDEN, Nathan
Arrangement: Im Hyun-sik, EDEN, Nathan

9) iKON - RHYTHM TA

Album: Welcome Back (2015)
Lyrics: B.I, Bobby
Composition: B.I, June, FUTURE BOUNCE
Arrangement: FUTURE BOUNCE

iKON is also one of the gruops that gives their albums their own color, I wanted to add one of my favorite songs to the list.

8) B1A4 - Solo Day

Album: Solo Day (2014)

Lyrics: Jinyoung, Baro
Music: Jinyoung

Members produce all the song of their group, but since it's one of the iconic songs, I chose Solo Day to put it on the list.

7) WINNER - REALLY REALLY

Album: Fate Number For (2017)
Lyrics: Yoon, Mino, Hoony
Composition: Mino, Yoon, Kang Uk-jin
Arrangement: Kang Uk-jin

WINNER also has a group that makes all their songs but I wanted to put this song, that makes them born from the ashes, on the list.

6) BLOCK B - H.E.R

Album: H.E.R (2014)
Lyrics: Zico
Music: Zico, Pop Time

Almost all the title songs of Block B also produce by members, but I wanted to put the song "H.E.R" on the list, which was a big hit.

5) DAY6 - Shoot Me

Album: Shoot Me: Youth Part 1 (2018)
Lyrics: Young K
Composition: Young K, Wonpil, Jae, Sungjin, Hong Ji-sang, Lee Woo-min
Arrangement: Hong Ji-sang, Lee Woo-min

As expected from a band group, they make their own songs. But I wanted to put "Shoot Me" on the list, which I listened a lot last year.

4) JYJ - In Heaven

Album: In Heaven (2011)
Lyrics: Kim Jaejoong
Composition: Kim Jaejoong
Arrangement: BJD, MDS

All the albums of the group are produced by the members but I wanted to put "In Heaven" on the list because the lyrics of this song enshrine in my heart.. The lyrics of the song "Get Out" also belonged to Kim Jaejoong and Park Yoochun; the song was composed by these two members.

3) 2PM - Go Crazy!

Album: Go Crazy! (2014)
Lyrics: Jun. K
Composition: Jun. K, Danny Majic, DJ Nure, Fingazz, Dustin Tavella
Arrangement: Jun. K, Danny Majic, DJ Nure, Fingazz, Dustin Tavella

Jun.K has played an active role in the b-sides of the group, and after their rookie period, we see that he also took part in the title tracks. "My House" is another title song written by Jun.K but I wanted to add my favourite 2PM song Go Crazy to the list.

2) BIGBANG - Haru Haru

Album: Stand Up (2008)
Lyrics: G-Dragon
Composition: G-Dragon, Daishi Dance
Arrangement: Daishi Dance

The song is written by G-Dragon, the main songwriter and composer of their most of songs. Since Haru Haru was a song from their rookie period and one of the group's hit songs, I chose Haru Haru to put it on the list.

1) CNBLUE - Cinderella

Album: 2gether (2015)
Lyrics: Jung Yong-hwa
Composition: Jung Yong-hwa
Arrangement: Jung Yong-hwa, Lee Sang-ho

The main songwriter, composer and arranger of the song is Yong Hwa. But Yong Hwa is a member of the group that gives color to their all albums.

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Same groups haveother title songs that I didn't add to the list, but written by members. You can add as comments if you wish.

Source: komca + wikipedia + youtube

(* Accuracy of all data has been checked from Komca.)