Mich. Comp. Laws § 722.26c

Sec. 6c. (1) A third person may bring an action for custody of a child if the court finds either of the following: (a) Both of the following: (i) The child was placed for adoption with the third person under the adoption laws of this or another state, and the placement order is still in effect at the time the action is filed. (ii) After the placement, the child has resided with the third person for a minimum of 6 months. (b) All of the following: (i) The child's biological parents have never been married to one another. (ii) The child's parent who has custody of the child dies or is missing and the other parent has not been granted legal custody under court order. (iii) The third person is related to the child within the fifth degree by marriage, blood, or adoption. (2) A third person shall include with an action filed under this section both of the following: (a) An affidavit setting forth facts relative to the existence of the prerequisites required by subsection (1)(a) or (b). (b) Notice that a defense or objection to a third person's right to bring an action for custody may be raised as an affirmative defense or by a motion for summary disposition based on lack of standing as provided in the Michigan court rules.