More info : https://www.doujinshi.org/book/326901/Kyokumen-Oppai-Double/ https://www.toranoana.jp/mailorder/article/04/0010/24/30/040010243048.html http://www.suruga-ya.jp/product/detail/ZHOA22880
So, Tomoki used the Metamorphosis Machine to make his dick bigger so that he could get Ikaros to titfuck him. His hardon stayed hard afterwards, so Ikaros used what she learned from porn books to solve the problem, meaning she fucked him. Then Sohara showed up at the climax, but instead of going ballistic, she decided she wanted the D. Ikaros lent a hand (tongue actually). Once Tomoki was done with Sohara, Ikaros checked him out with the computer and found that the energy from the Metamorphosis Machine left behind in his body was about to go critical - meaning, his dick was about to literally explode.