nearest relative; next of kin
Formal term used in legal, inheritance, or medical contexts to refer to the closest blood relative.
Please write the name of your nearest relative as an emergency contact.
The estate is inherited by the next of kin.
近親者 means a close relative, but 最近親 emphasizes the single nearest relative, often in legal contexts.
Compound of 最 (most) + 近親 (close relative). The exact historical derivation is uncertain, but the term is used in modern legal and formal Japanese.