The matters specified by Ministry of Finance Order as prescribed in Article 263, paragraph (1) (Special Provisions on Tax Returns in the Case of Death) of the Order are the following:
令第二百六十三条第一項（死亡の場合の確定申告の特例）に規定する財務省令で定める事項は、次に掲げる事項とする。
the name, domicile (where the person has no domicile in Japan, the residence; hereinafter the same in this item) and individual number (for a person who has no individual number, the name and domicile) of each heir, the relationship to the decedent, the share of inheritance of that heir under the provisions of Articles 900 to 902 (Statutory Inheritance Shares, Inheritance Shares of Heirs by Representation, and Designation of Inheritance Shares by Will) of the Civil Code (Act No. 89 of 1896), and the value of the property obtained by inheritance or bequest;
各相続人の氏名、住所（国内に住所がない場合には、居所。以下この号において同じ。）及び個人番号（個人番号を有しない者にあつては、氏名及び住所）、被相続人との続柄、民法（明治二十九年法律第八十九号）第九百条から第九百二条まで（法定相続分・代襲相続人の相続分・遺言による相続分の指定）の規定によるその相続分並びに相続又は遺贈によつて得た財産の価額
if there are two or more heirs, the amount of income tax equivalent to the amount calculated by apportioning the amount of income tax set out in Article 120, paragraph (1), item (iii) (Filing Income Tax Returns) of the Act (where there is a withheld tax amount prescribed in item (iv) of that paragraph and there is no prepaid tax amount prescribed in item (v) of that paragraph, the amount set out in item (iv) of that paragraph, and where there is a prepaid tax amount prescribed in item (v) of that paragraph, the amount set out in that item) according to the share of inheritance of each heir in item (i);
Where the return prescribed in Article 263, paragraph (2) of the Order is submitted by the method set out in the proviso to that paragraph, it is not required to state in that return the individual number of another heir whose name is added pursuant to the proviso to Article 263, paragraph (2) of the Order, among the matters set out in item (i) of the preceding paragraph.
定義第一条の五第一項
行政手続における特定の個人を識別するための番号の利用等に関する法律（平成二十五年法律第二十七号）第二条第五項（定義）に規定する個人番号
わかりやすく言うと
住民票コードを変換して得られる番号で、その住民票に記載された人を識別するために指定されるものです（行政手続における特定の個人を識別するための番号の利用等に関する法律第二条第五項）。