TT #657 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:05
When brothers dwell together and one of them dies and has no son, the wife of the dead shall not be outside to a strange man; her husband’s brother shall come upon her and take her to himself as a wife and perform the duty of a husband’s brother for her.
Torah Temimah points to Kiddushin 14a.
TT lemma: יְבָמָהּ יָבֹא עָלֶיהָ.
יְבָמָהּ יָבֹא עָלֶיהָ – הַיְּבָמָה נִקְנֵית בְּבִיאָה.
English: “Her yavam shall come upon her” — the yevamah is acquired by the act of intercourse.
On the daf / in context: The primary mode of acquisition in yibbum is bi’ah; the verse itself establishes the legal mechanism.
Derash identifying the mode of acquisition.
Yibbum is effected by the act of intercourse itself.