The Green Snake Demon flung out her black lace undergarment, which transformed into a black butterfly. Using skill over strength, she finally captured the eldest son.
Version 1.71 adds an extra 10 seconds of footage showing the eldest child fighting the black butterfly, building upon version 1.6.
15-second preview: Big Baby vs. Black Butterfly Version 1.6 - Bilibili
Script (the difference is that the R-18 scene was removed in the video): Big Brother vs. Black Butterfly (Script Draft) - Fansky
(Published on Bilibili during the Spring Festival, it garnered over 100,000 views but was taken down due to its negative impact.)