Exhibit 5.1

December 23, 2025

FiEE, Inc.

Flat A1, 29/F, Block A, TML Tower

Hoi Shing Road, Tsuen Wan, Hong Kong

Ladies and Gentlemen:

We have acted as special counsel to FiEE, Inc., a Delaware corporation (the “Company”), in connection with the Registration Statement on Form S-8 filed on the date hereof (the “Registration Statement”) with the U.S. Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), for the registration of 1,394,230 shares of Common Stock, par value $0.01 per share, of the Company (“Common Stock”), available for issuance or transfer pursuant to awards made under that certain FiEE, Inc. 2025 Equity Incentive Plan (the “Plan”).

You have requested our opinion as to the matters set forth below in connection with the Registration Statement. For purposes of rendering that opinion, we have reviewed: (a) the Registration Statement; (b) the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State of the State of Delaware (the “Secretary of State”) on September 22, 2009, as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on November 16, 2015, as amended by the Certificate of Designation of Series A Junior Participating Preferred Stock of the Company as filed with the Secretary of State on November 16, 2015, as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on July 25, 2019, as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on June 2, 2021 (the “June 2, 2021 Amendment”), as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on June 3, 2021, as corrected by the Certificate of Correction of Certificate of Amendment of the Company as filed with the Secretary of State on June 30, 2021 nullifying the June 2, 2021 Amendment, as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on July 23, 2021, as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on March 31, 2023, as amended by the Certificate of Designations, Preferences, Rights, and Limitations of Series A Convertible Preferred Stock of the Company as filed with the Secretary of State on January 26, 2024, as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on March 6, 2024, as amended by the Amended and Restated Certificate of Designations, Preferences, Rights, and

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Limitations of Series A Convertible Preferred Stock of the Company as filed with the Secretary of State on October 8, 2024, as amended by the Certificate of Amendment to the Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on February 27, 2025, and as amended by the Certificate of Amendment of Amended and Restated Certificate of Incorporation of the Company as filed with the Secretary of State on August 1, 2025, providing for the Second Amended and Restated Certificate of Designations, Preferences, Rights, and Limitations of Series A Convertible Preferred Stock of the Company; (c) the Second Amended and Restated Bylaws of the Company adopted March 28, 2025; (d) the Plan; (e) the Action by Unanimous Written Consent of the Compensation Committee of the Board of Directors of the Company (the “Compensation Committee”) adopted on September 8, 2025 approving, and submitting to the Board of Directors of the Company (the “Board of Directors”) for approval, the Plan; (f) the Action by Unanimous Written Consent of the Board of Directors of the Company adopted on September 8, 2025 approving the Plan, including the provision of 1,394,230 shares of Common Stock (collectively, the “Shares” and each, a “Share”) for issuance or transfer pursuant to awards made under the Plan; (g) the Minutes of the 2025 Annual Meeting of Stockholders of the Company held on October 27, 2025, at which annual meeting the Company’s stockholders approved the Plan; and (h) a certificate of an officer of the Company, dated as of the date hereof, with respect to certain matters. Other than our review of the documents listed in (a) through (h) above (collectively, the “Reviewed Documents”), we have not reviewed any other documents or made any independent investigation for the purpose of rendering this opinion.

For purposes of rendering our opinion below, we have not reviewed any document other than the Reviewed Documents and assume there exists no provision in any document relating to the matters covered by our opinion below that we have not reviewed that is inconsistent with the Reviewed Documents or our opinion below. We have conducted no independent factual investigation of our own but rather have relied on the Reviewed Documents, the statements and information set forth therein, and the additional matters recited or assumed herein, all of which we assume to be true, complete, and accurate in all respects.

For purposes of this opinion letter, we have assumed that: (a) each of the Reviewed Documents is accurate and complete; (b) each Reviewed Document that is an original is authentic; (c) each Reviewed Document that is a copy conforms to an authentic original; (d) all signatures on each Reviewed Document are genuine; and (e) the Company is and shall remain at all times a corporation duly incorporated, validly existing, and in good standing under the laws of the State of Delaware. We have further assumed: (i) the legal capacity of natural persons; (ii) that each party to the Reviewed Documents (A) is duly formed or incorporated, organized, validly existing, and in good standing under the laws of the state of its formation or incorporation, (B) has the legal capacity, power, and authority to execute, deliver, and perform its obligations under the Reviewed Documents to which it is a party, (C) has taken all action necessary to authorize the execution and delivery of, and the performance of such party’s obligations under, the Reviewed Documents to which it is a party, and (D) has duly executed and delivered the Reviewed Documents to which it is a party; (iii) that any amendment and/or restatement of any of the Reviewed Documents was accomplished in accordance with, and was permitted by, the relevant provisions of such document and applicable law; (iv) that the issuance of the Shares will not (A) result in the issuance of Shares to an “interested stockholder” (within the meaning of Section 203(c) of the General Corporation Law of the State of Delaware (the “DGCL”) and hereinafter referred to as an “Interested Stockholder”), (B) increase the proportionate share of Common Stock or other securities held by an Interested Stockholder, or (C) confer a benefit, directly or indirectly (except proportionally as a stockholder of the Company) of any financial benefit (other than those expressly permitted by Section 203(c)(3)(i)–(iv) of the DGCL) on an Interested Stockholder; and (vi) that there are no contracts with one or more current or prospective stockholders of the Company (or one or more beneficial owners of stock of the Company), in its or their capacity as such, within the meaning of Section 122(18) of the DGCL. We have not verified any of the foregoing assumptions.

In rendering our opinion below, we also have assumed that: (a) the Company will have sufficient authorized, unissued, and unreserved shares of Common Stock at the time of each issuance of any Shares or rights or options to acquire Shares, in each case, under the Plan; (b) either (i) upon the issuance of a Share, such Share will be evidenced by a certificate that has been duly executed and delivered, or (ii) the Board of Directors will have adopted a resolution (that has not been rescinded or revoked) providing that all shares of Common Stock shall be uncertificated in accordance with Section 158 of the DGCL prior to the issuance of a Share and, within a reasonable time after the issuance of any such uncertificated Share, the registered owner of such Share will be given notice in writing or by electronic transmission in compliance with Section 151(f) of the DGCL; (c) the issuance of each Share will be duly recorded in the Company’s stock ledger upon its issuance; (d) the Plan and each Award Agreement (as defined in the Plan and hereinafter referred to as an “Award Agreement”) constitutes or will constitute, as applicable, the valid and binding agreement of the Company, enforceable against the Company in accordance with its terms; (e) the Company will receive consideration for each Share as set forth in the Authorizing Resolutions (as defined below), which consideration shall be at least equal to the par value of such share of Common Stock (unless such Share is held in treasury, in which case, the consideration shall be the amount as set forth in the Authorizing Resolutions), and, in the amount required by the Plan and the applicable Award Agreement; (f) with respect to any Shares issuable upon the exercise of any right or option to acquire Shares under the Plan, the Company shall have received the minimum consideration for which such rights or options may be issued pursuant to the Authorizing Resolutions, the Plan, and the applicable Award Agreements; and (g) prior to the issuance of any Shares (or any right or option to acquire any Shares) under the Plan, the Board of Directors, the Compensation Committee, or another duly authorized committee or subcommittee of the Board of Directors will duly authorize each Award (as defined in the Plan) granted under the Plan with respect to which Shares are issuable pursuant to an Award Agreement and in accordance with the DGCL and the Plan (the “Authorizing Resolutions”). We have not verified any of the foregoing assumptions.

Our opinion set forth below is limited to the DGCL and reported judicial decisions interpreting the DGCL. We express no opinion as to the laws, rules, or regulations of any other jurisdiction, including, without limitation, the federal laws of the United States of America or any state securities or blue sky laws.

Based upon and subject to the foregoing, and assuming that the Registration Statement is effective at the time of issuance of the Shares, it is our opinion that the Shares, when and if issued pursuant to the terms of the Plan, the Authorizing Resolutions, and the applicable Award Agreement, will be validly issued, fully paid, and non-assessable.

This opinion is expressed as of the date hereof, and we disclaim any undertaking to advise you of any subsequent changes in the facts stated or assumed herein or of any subsequent changes in applicable laws.

We hereby consent to the filing of this opinion letter with the Commission as Exhibit 5.1 to the Registration Statement. In giving the foregoing consent, we do not thereby admit that we are experts with respect to any part of the Registration Statement within the meaning of the term “expert” as used in Section 11 of the Securities Act or the rules and regulations promulgated thereunder, nor do we admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.