Main characters
- Lee Hyeri as Sung Deok-sun
- The middle child of her family, she is not very bright in studies and is the only girl in their group of five neighborhood friends.
- Ryu Jun-yeol as Kim Jung-hwan
- Stoic and sarcastic, grumbles a lot, loves soccer and also one of the top students in school. He harbors a crush for Deok-sun.
- Park Bo-gum as Choi Taek
- A genius baduk player who is mostly quiet and struggles with simple day-to-day tasks. He likes Deok-sun.
- Go Kyung-pyo as Sung Sun-woo
- A caring brother and a dependable son to his family.
- Lee Dong-hwi as Ryu Dong-ryong
- The geek of the group, but more knowledgeable about girls and life in general.
Supporting characters
- Sung family
- Sung Dong-il as Sung Dong-il (Deok-sun's father)
- Lee Il-hwa as Lee Il-hwa (Deok-sun's mother)
- Ryu Hye-young as Sung Bo-ra (Deok-sun's older sister)
- Has a warm heart beneath her stubborn, ill-tempered exterior. Active in the student protest movement and a student at Seoul National University.
- Choi Sung-won as Sung No-eul (Deok-sun's younger brother)
- Despite being the youngest child of the Sung family, he looks much older than his age.
- Kim family
- Kim Sung-kyun as Kim Sung-kyun (Jung-hwan's father)
- Ra Mi-ran as Ra Mi-ran (Jung-hwan's mother)
- Ahn Jae-hong as Kim Jung-bong (Jung-hwan's older brother)
- Sun-woo family
- Kim Sun-young as Kim Sun-young (Sun-woo's mother)
- Kim Seol as Sung Jin-joo (Sun-woo's little sister)
- Neighborhood residents
- Choi Moo-sung as Choi Moo-sung (Taek's father)
- Yoo Jae-myung as Ryu Jae-myung (Dong-ryong's father)
- Extended cast
- Lee Min-ji as Jang Mi-ok (Deok-sun's friend)
- Lee Se-young as Wang Ja-hyun (Deok-sun's friend)
- Kim Tae-soo as Sun-young's older brother
- Lee Mi-yeon as adult Sung Deok-sun
- Kim Joo-hyuk as Husband of adult Sung Deok-sun [8]
- Jeon Mi-seon as adult Sung Bo-ra
- Woo Hyun as adult Sung No-eul
Cameo and guest appearances
- Kim Young-ok as Deok-sun's grandmother (ep. 2)
- Jung Won-joong as Dong-il's older brother (ep. 2)
- Kim Su-ro as snack shop owner (ep. 3)
- Lee Moon-se (voice) as radio DJ (ep. 6)
- Park Ji-yoon as TV interviewer (ep. 7)
- Park Jung-min as Bo-ra's boyfriend (ep. 8)
- Kim Tae-hoon as Cardiac surgeon (ep. 8)
- Lee Soo-kyung as No-eul's girlfriend (ep. 8)
- Jung Yoo-min as Bo-ra's friend (ep. 8)
- Jung Hae-in as Ho-young, Deok-sun's middle school friend (ep. 13)
- Shin Young-jin as Class President's mother (ep.14)
- Jung Woo as Kim Jae-joon/Trash (ep.18)
- Go Ara as Sung Na-Jung (ep.18)
- Episode 1 - 20 (engsub / indsub)
- Episode 1
- Episode 2
- Episode 3
- Episode 4
- Episode 5
- Episode 6
- Episode 7
- Episode 8
- Episode 9
- Episode 10
- Episode 11
- Uptobox | Mega | Solidfiles
- Episode 12
- Uptobox | Mega | Solidfiles
- Episode 13
- Uptobox | Mega | Solidfiles
- Episode 14
- Uptobox | Mega | Solidfiles
- Episode 15
- Uptobox | Mega | Solidfiles
- Episode 16
- Uptobox | Mega | Solidfiles
- Episode 17
- Uptobox | Mega | Solidfiles
- Episode 18
- Uptobox | Mega | Solidfiles
- Episode 19
- Uptobox | Mega | Solidfiles
- Episode 20
- Uptobox | Mega | Solidfiles
