They are brothers
One is the bargaining chip that the mother had to pay in order to gain freedom.
One is an orphan whose mother reluctantly abandoned her in order to pursue love.
They all long for warmth because they rarely get it
Until they met, met under the wish of their common mother before she died.
They go from unfamiliarity to familiarity; from misunderstanding to trust; from indifference to tolerance.
It was not until after experiencing a lot that they became relatives, friends, and lovers; they became the closest people who would always be with each other and never abandon each other.