Sec Form 4 Filing - TAKEDA PHARMACEUTICAL CO LTD @ Day One Biopharmaceuticals, Inc. - 2021-11-24

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person TAKEDA PHARMACEUTICAL CO LTD 2. Issuer Name and Ticker or Trading Symbol Day One Biopharmaceuticals, Inc. [ DAWN] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 1-1, NIHONBASHI-HONCHO 2-CHOME 3. Date of Earliest Transaction (MM/DD/YY) 11/24/2021 (Street) CHUO-KU, TOKYO, M0103-8668 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 11/24/2021 J( 1 ) 57,224 A $ 0 6,527,606 I See Explanation of Responses( 2 )( 3 )( 4 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other TAKEDA PHARMACEUTICAL CO LTD 1-1, NIHONBASHI-HONCHO 2-CHOME CHUO-KU, TOKYO, M0103-8668 X Takeda Pharmaceuticals U.S.A., Inc. 95 HAYDEN AVENUE LEXINGTON, MA02421 X MILLENNIUM PHARMACEUTICALS INC 40 LANDSDOWNE STREET CAMBRIDGE, MA02139 X Takeda Ventures, Inc. 9625 TOWNE CENTRE DRIVE SAN DIEGO, CA92121 X Signatures /s/ Yoshihiro Nakagawa, Corporate Officer, GlobalGeneral Counsel of Takeda Pharmaceutical CompanyLimited 11/29/2021 Signature of Reporting Person Date /s/ Paul Sundberg, Assistant Secretary of Takeda Pharmaceuticals U.S.A., Inc. 11/29/2021 Signature of Reporting Person Date /s/ Paul Sundberg, Attorney-in-Fact for Millennium Pharmaceuticals, Inc. 11/29/2021 Signature of Reporting Person Date /s/ Michael Martin, President of Takeda Ventures, Inc. 11/29/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On November 24, 2021, Takeda Ventures, Inc., a subsidiary of Takeda Pharmaceutical Company Limited, received a distribution of 57,224 shares of Common Stock (the "distribution") from Atlas Venture Fund XI, L.P. Takeda Ventures, Inc. is a limited partner of Atlas Venture Fund XI, L.P. The distribution was a pro-rata distribution, and not a purchase or sale, without any consideration paid by Takeda Ventures, Inc. ( 2 )This statement is being filed jointly by Takeda Pharmaceutical Company Limited, Takeda Pharmaceuticals U.S.A. Inc., Millennium Pharmaceuticals, Inc. and Takeda Ventures, Inc. ( 3 )Takeda Pharmaceutical Company Limited's beneficial ownership of the reported securities is comprised of 6,470,382 shares of Common Stock held by Millennium Pharmaceuticals, Inc. and 57,224 shares of Common Stock held by Takeda Ventures, Inc. Millennium Pharmaceuticals, Inc. and Takeda Ventures, Inc. are each direct, wholly owned subsidiaries of Takeda Pharmaceuticals U.S.A. Inc., which is a direct subsidiary of Takeda Pharmaceutical Company Limited (72.70%) and Takeda Pharmaceuticals International AG (27.3%). ( 4 )Takeda Pharmaceuticals International AG is a direct, wholly owned subsidiary of Takeda Pharmaceutical Company Limited. Each of Takeda Pharmaceutical Company Limited and Takeda Pharmaceuticals U.S.A. Inc. may be deemed to share voting and dispositive power over the shares held by Takeda Ventures, Inc. and Millennium Pharmaceuticals, Inc. Each of Takeda Pharmaceutical Company Limited and Takeda Pharmaceuticals U.S.A. Inc. disclaims beneficial ownership of the shares held by Takeda Ventures, Inc. and Millennium Pharmaceuticals, Inc. except to the extent of their pecuniary interests therein.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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