いもうとimouto
1.

A term used to refer to a female sibling born to the same parents as the speaker, typically younger than the speaker, encompassing both biological and some cultural contexts.

2.

A respectful or affectionate designation for a woman's younger sister, which can also extend to indicate a close relationship with a female whom one feels a bond, such as a daughter-in-law or a younger female companion.

3.

In certain contexts, it can refer to a man's girlfriend or wife, showcasing the intimacy of the relationship through familial terminology.

4.

Historically used to address or refer to a younger female relative or close female acquaintance, often reflecting societal norms or affectionate bonds in traditional literature.

Example:

あのかわいい少女は私のです。

しまい姉妹shimaiきょうだい姉妹kyoudai
1.

Refers to a female sibling, specifically the relationship between an older sister and a younger sister within a family structure.

2.

Describes two or more entities that share similarities or are equivalent in nature or function, often used in contexts such as organizations, products, or cultural institutions that have common origins or purposes.

3.

Represents the concept of sisterhood not strictly in familial terms, but also in expressions of affinity, solidarity, or partnership between two or more items or groups.

Example:

彼の姉妹は二人とも美人です。

けいまい兄妹keimaiきょうだい兄妹kyoudai
1.

A relationship between an older male sibling and a younger female sibling, often characterized by care, protection, and guidance from the brother toward the sister.

2.

A familial connection that signifies the bond between an elder brother and his younger sister, including shared upbringing and mutual support.

3.

A specific pairing of siblings where one is male and the other is female, representing a traditional family structure with distinct roles.

4.

A term that captures the dynamic interplay of affection, responsibility, and rivalry that can occur between a brother and sister in a family setting.

Example:

「でも、俺たち兄妹だろ!」「名目上ではね」

いもうとimoutoさんsan
1.

A term used to refer to someone's younger sister in a respectful or affectionate manner, often used to indicate a familial bond and care within family relationships.

2.

A way to address or refer to a girl or woman who is younger than oneself, emphasizing a relationship that may involve nurturing or mentoring.

3.

A polite expression for addressing or discussing a younger female sibling, commonly used in various contexts to convey warmth or closeness in family dynamics.

Example:

妹さんが手術後危機を脱したそうで、よかったですね。

ぎまい義妹gimaiいもうと義妹imouto
1.

A woman who is considered a younger sister due to a formal or symbolic agreement, often signifying a close relationship beyond mere familial ties.

2.

A female relative acquired through marriage or familial connections, such as a brother's wife or a spouse's sister, emphasizing the bond created by these relationships rather than blood ties.