Dazai is Chin's 2nd adoptive son, who gets hurt very often but Chin is always there to comfort him.

(Background)

Dazai was born on June 19, 2006 in the forest. His mother abandoned him, after his father died from drowning and was raised in the Yokohama orphanage . Which made Dazai want to seek the light just like Kyouka does.

One night no Christmas in 2011, the other children overheard a conversation of the nun sending the aku siblings out for adoption.

When they got out of the room, the men saw them and started beating all of the children except for Kunikida, Chuuya, the Aku siblings and him, who managed to escape.

Birthday: June 19, 2006

Age: 10 - 11 (First appearance), 12 (Time skip), 13 (Currently)

Personality: While in the present he is more suicidal, lighthearted and comical, he still retains some of his darker personality.

Relatives: Chikan (Biological mother, Deceased), Unnamed biological father (Deceased), Henko (Biological grandmother)

Chin Xi (Adoptive mother), Yukichi (Adoptive father), Mori (Adoptive great-uncle), Akiko (Older adoptive sister), Ryu Aku (Adoptive Brother), Gin Aku (Adoptive Sister), More younger/older adoptive siblings

Occupation: Orphan (Formerly), Big brother figure (Currently)

Affiliation: Yokohama orphanage (Formerly, Escaped) Sai ijō no kodomo no ie and the sailor agency (Currently)

Relationship with Chin: Dazai also has the nerves to call Chin "Mommy or Mum" 

Wiki references if you've never heard of this character: https://bungostraydogs.fandom.com/wiki/Osamu_Dazai