noun
sister complex; excessive attachment to one's sister
Refers to an unusually strong emotional dependence on or obsession with one's sister, often used in psychological or colloquial contexts. Similar in construction to 'mother complex' (マザーコンプレックス).
彼はシスターコンプレックスで、妹の結婚を素直に喜べなかった。
He has a sister complex and couldn't wholeheartedly celebrate his younger sister's marriage.
シスターコンプレックスが強いと、姉に彼氏ができると嫉妬してしまうこともある。
When someone has a strong sister complex, they may feel jealous if their older sister gets a boyfriend.