In Aika Zero, we have the emergence of an alien antagonist. We do not know much about the alien. It seems that its main purpose was to go to earth to retrieve genetic data about humans. It's first victim was either Miyu Shiratori or E.T.A.I.. It was probably E.T.A.I. though, because she is the stronger one and seems to be in higher command than Miyu.
In the beginning of the episode, White Knights Miyu Shiratori is investigating what seems to be an alien structure. As she gets deep inside, a string of yellow tendril. It gets close to her, then moves from the floor into the air directly below her. It penetrates her by shooting straight up into her butt. The penetration causes a quick loss of consciousness and she falls to the ground. More tendrils come to lift her up and into the alien structure. It is supposed that this was E.T.A.I.'s first probing of humans.
Soon after this, Miyu also has three other girls in the White Knights. Three other girls come from the school to the chapel. They are wearing black, which means they are not White Knights yet. Miyu thanks the girls for coming, then the three White Knights she is with start to molest the recruits. The recruits put up little fight, and then we see an Alien tendril come in the room through a window, it quickly splits into three tendrils and heads for the girls. Each girl is penetrated simultaneously by the tendrils. This is the only time in the anime where we can actually see each girl's butt cheeks stiffen up, then relax as she falls unconscious. The girls are then examined by the tendril and pulled up into the ceiling.
At the end of the episode, Aika infiltrates the chapel and finds a bunch of girls suspended in the air by the tendrils. Aika soon gets ambushed by Miyu, and is strangled by the tendrils. She is almost penetrated, but is recued by Risako.
In the beginning of the episode, E.T.A.I., we see the story of how Miyu found the alien structure. She was led by the alien tendrils. We are then taken to a swim meet, where Miyu is facing Kana Shiraishi, the school champion. Miyu beats Kana handily, much to Kana's surprise.
Then we are taken to the school hallway where the scores for the highest grades have been posted on the wall. the girls all think that it will be Rin Shiragiku at the top of the list, but Rin herself is surprised to see that Miyu Shiratori is at the top of the list.
After Kana and Rin were bested by Miyu, they were eager to join this prestigious club that Miyu was forming. Miyu brings them to the chapel were she tells them to bend over and hike their skirts up. The Alien tendrils then penetrate Kana and Rin and knock them out. They thus become the first members of the White Knights.
In the next scene, Misumi is unconscious and bent over the back of the couch. The Alien Tendrils are attached to her along her spinal column. Also unconscious is the dark-haired white knight. E.T.A.I. then sends a tendril to penetrate the blond haired girl. After she is penetrated, Kana and Rin, carry the dark haired girl and the blonde girl over and bend them over the couch just like Misumi. The alien tendrils then attach to those two. Kana and Rin then get the surprise of seeing an alien tendril coming for each of them. They are told that it is "for insurance" as they are both bent over a couch. They are both knocked out by a tendril.