A return form pursuant to the provisions of Article 124, paragraph (1) or (2) (Filing a Tax Return If the Person Required to File Has Died) or Article 125, paragraphs (1) through (3) (Filing a Tax Return If the Taxpayer Has Died Partway Through the Year) of the Act must state, in addition to the matters listed in the items of Article 120, paragraph (1) (Filing an Income Tax Return) or the items of Article 122, paragraph (1) (Filing a Return to Receive a Refund) of the Act, the matters specified by Ministry of Finance Order; in this case, the provisions of the second sentence of Article 120, paragraph (1) of the Act apply mutatis mutandis to the return form pursuant to the provisions of Article 124, paragraph (1) or (2) of the Act.
法第百二十四条第一項若しくは第二項（確定申告書を提出すべき者等が死亡した場合の確定申告）又は第百二十五条第一項から第三項まで（年の中途で死亡した場合の確定申告）の規定による申告書には、法第百二十条第一項各号（確定所得申告）又は第百二十二条第一項各号（還付等を受けるための申告）に掲げる事項のほか、財務省令で定める事項を併せて記載しなければならない。この場合において、法第百二十四条第一項又は第二項の規定による申告書については、法第百二十条第一項後段の規定を準用する。
Where the return form under the preceding paragraph is submitted and there are two or more heirs, that return form must be submitted by each heir in a single document bearing their joint signatures; provided, however, that this does not preclude the forms from being submitted separately with the names of the other heirs added.
An heir who has submitted the return form prescribed in the preceding paragraph by the method under the proviso to that paragraph must, without delay, notify the other heirs of the outline of the matters stated in that return form.
Read this with the articles around it
heirmachine translation
「相続人」
An heir, including, wherever this Cabinet Order uses the word, a universal legatee (包括受遺者): a person to whom a will leaves all or a share of an estate as a whole, rather than particular property.
Defined inArticle 1, paragraph (3)· applies throughout the law