In the original anime, Ritsuko was ordered to report to SEELE naked so those perverted old men could gawk at her. They know it's going to upset her and they do it partially because of that. It's very blatant that she is an object to them, there for their viewing pleasure and to be used as a tool.
SEELE is already a creepy death cult: given how they treat Ritsuko, think about how they'd act if they were a creepy Satanic cult instead. Yeah. Oh, by the way, in the second draft of episode 24 (Anno's first rewrite - he got someone with experience writing Boys Love to do the first draft for him), it's revealed that Gendo has been having sex with Rei as a Yui substitute. The Second Draft of that episode is very worth reading for anyone trying to decipher the series.
Eva uses nudity and inappropriate sexualization and sexual activity for shock value in order to hammer home a point, like trying to make sure sure the watcher feels the appropriate squick, very often. EoE is chock full of it, especially the scene meant to demonstrate that Shinji doesn't love or even respect Asuka as a person at all (by that point) in an absolutely disgusting way.
There's also 2.22, the Reiquarium, Gendo basically whoring himself out to the Akagis so he could use 'the old hag' and Ritsuko's feelings to control them and get Yui her godhood... There's a lot of sexualization in Eva that is meant to be inappropriate, although that doesn't keep people from fetishizing scenes written to be absolutely disgusting (the EoE hospital scene being the chief offender).
When you add a setting and premise like this to an Original Flavor like that...
Note that in this time period in England, it was legal for a boy to marry (not just 'start having sex' but marry and gain access to sex whenever they wanted) at fourteen, which is why Tabris set that as the minimum age at which someone could sell their soul - marriage is a sacrament that involves transfer of ownership of people, so it amused him to frame the sale of souls into eternal bondage as an unholy parody of it.
Girls could be married off at twelve, which is why Asuka could make her pact and start practicing magic a couple years ago (and she would have been vulnerable to one of the other circle members hitting her with a spell to marry them or one of their sons if she hadn't pacted and Mari hadn't made arrangements). From Tabris' perspective, all humans are younger than he is, so he's going by the local culture's definition of when people are old enough to sell themselves into bondage, and also what is and is not child abuse/statutory rape.
By Victorian standards, Shinji is perfectly legal. It's just that those standards were messed up, and actually a giant step backwards: before 1823, the minimum age for marriage was 21 for men and women both.
When he found Hikari, almost babbling as he asked her if he was late and told her he was really very sorry if he was, she told him that was alright. "There's always alchemy that needs doing around the house, and Kaji's always happy to have an excuse to lie about the house, although I think he'll be grateful to us for rescuing him from Asuka."
She led him into a sunlit room, where a blonde woman was sorting through rolls of fabric and casting an annoyed glance at a somewhat scruffy-looking man, who wasn't clean shaven despite wearing the costume of a young professional about town. The costume was somewhat scruffy in an artful way, and Shinji thought it might have been even before the red-headed young woman who looked about Shinji's age forced him to his knees and grabbed him by his cravat.
"Asuka," the last person in the room sing-songed. "Don't you think it's time to let him go? We have company." She grinned at Shinji, who noted the cat ears in her hair, the lashing tail. Yet, despite the smile, he didn't think this person was all that happy with what was going on? Or just what was going on when they came in.
She spun around to look at them crossly, but when she saw Hikari her expression softened, or at least she looked understanding. "Hikari."
"Mistress Asuka." Hikari bowed. "Mistress Asuka, this is Master Tabris' new familiar."
"A Keel," she said, scowling at him.
"A Keel?" Shinji blinked, trying to look harmless. So this was the witch? And the cat had to be Mari. Who was already a demon.
"Lorenz Keel. The founder of SEELE. He funded the Katsuragi expe-but you don't know anything, do you." Her scowl deepened. "You might have gotten a chance to get Master Tabris' favor, entirely undeserved, but you're not a man, you're a catamite. You won't be able to get any real power, not any more than he has." She kicked Kaji in the side.
Not all that hard, it seemed: Kaji just looked embarrassed for Asuka more than anything. That slight wince wasn't on his own behalf. "Hi, I'm Kaji," he said, standing up, dusting himself off and giving him a winning smile. "You're a cute little thing, aren't you? Why don't we grab something from the kitchens and have tea out in the garden after we're done here?"
"But, but I'm Master Tabris', and I don't think he'd want me... Unless he wants infidelity?" Shinji realized, suddenly worried. Kaji sleeping with someone else's woman, or kept boy in this case, would violate one of the ten commandments, which a devil would want, but jealousy was a deadly sin, so wouldn't Tabris have it and still be upset? He looked at Hikari, hoping she would help.
"Don't worry, Shinji," she told him. "Kaji has sold his soul to our master, but he's just a low-level warlock, barely a member of the Circle. He can't demand an incubus' services, and you're not just an incubus in training, you're our master's familiar. Kaji is a free agent, but that just means anyone with the authority can have him do whatever they want. In fact, our Master will probably instruct him to answer any questions you had about witches, warlocks and the powers they might have, since you're a contractor as well as a familiar. If you want to give him any other orders, ask me what you're allowed to command him to do. Or just ask him."
Kaji gave him a sweeping bow, and another smile laden with that roguish charm.
"I'm Ritsuko Akagi. I'm an alchemist and also a dressmaker, when it suits our Master's whims." Ritsuko's smile was more businesslike, although Shinji wondered if there was a bit of bitterness in it. "Go stand in the center of that room and drop that robe," she said, measuring tape ready to use.
Shinji obeyed, and when she saw his blush, she said, "Modesty, shame: if you don't lose them fast, you won't survive the circles." Shinji didn't think she was saying that to help him: the bitterness was even more apparent in her voice, and she knew she was just venting her feelings. This was the voice of experience. "In fact," she said, circling him thoughtfully. Before pinching his rear.
She went on to pinch his thighs, calves, arms, shoulders and other parts while Shinji was still standing there frozen in shock. Then she cupped her hands and put them over Shinji's chest. "A," she said, nodding. "I'll try that one first."
"Eh," Kaji said, "cut them for a small B. If it's too generous, he can pad them. Too small would be annoying to redo later."
"A?" Shinji asked, mystified.
"Breast sizes," Ritsuko said bluntly. "What kind of young man your age doesn't know pages of unrealistic information about breasts?"
"Catamite," was Asuka's assessment, tapping her foot and looking Shinji up and down with an air of absolute boredom. "Just like Hikari's mutt. She might have picked up one with some muscle on him, unlike this boy, but under his bluster he's a pure submissive."
Shocked that Asuka would say something like that in front of even one of the staff, Shinji turned to Hikari, only to see her nodding.
An arm was flung over his shoulder, and he found Mari sniffing his neck. "You smell like Master," she said, and purred. "Good incubi are either extremely submissive, like you and Touji, so they can enjoy the Circle doing whatever they want to them, or extremely dominant, like me, so we can enjoy making the Circle think they're doing what they want."
"Careful," Kaji said, amused. "You're giving away trade secrets."
"Says the man who serves… how many masters now?" Mari half-sang, waggling her finger at Kaji with a catlike smirk. She had whiskers, Shinji suddenly noticed, but then they vanished again.
"What can I say?" he said, spreading his hands. "I'm a man with needs."
"And yet he still refuses to submit to me! Part of the pact I made to get my familiar is that I can never be taken by a man," Asuka said proudly, hands on her hips. "So I'll just have to take Kaji myself!"
"Both of your mothers have asked me to look after you, Asuka," he reminded her. "You may be a full-grown witch now, but I still remember when you were a child."
"Excuse me, children," Ritsuko snapped, snapping her fingers in front of Mari's face. "Hands off the merchandise. Or have you forgotten whose familiar this is?"
"Aww, but you and yours can whip up pretty costumes in a snap," Mari teased, jumping away lightly.
"Yes, but first we need measurements and designs." Ritsuko cracked the measuring tape like a whip, and Shinji was the one who jumped back now, not sure where the flailing end would go. "Get back here," she told him, pointing to the spot on the ground. "Maya?!" she called, looking at a door to the right of where Shinji came in.
"Coming!" a female voice called, and another woman, older than Mari but younger than Ritsuko, ran in, carrying a stack of all different kinds of cloth.
"I need Kaji to consult with on the designs. I'm an alchemist, not a fashion plate. Anyone who can't contribute, out!"
"Don't look at me, I don't wear clothes when I can possibly get away with it," Mari said cheerfully, before jumping up towards Asuka. It was a brown cat that landed on Asuka's shoulder.
Asuka sniffed audibly, like a high society matron, before turning away. "I'm sure Hikari, unlike some people, has important business to attend to."
"Actually," the girl said as she followed Asuka out the door. "I was looking forward to spending some time with you. It's been too long since we had a chance to play a game."
"Splendid. Have one of your minions fetch the chess set."
Just like that, Shinji was the only person in the room not wearing clothes. Even the collared Maya was wearing a plain shift of heavy cotton, undyed except for what might be the remains of potion splashes. She smiled at him.
"She was a bright young woman, studying medicine even if they wouldn't give her a degree in order to help people," Ritsuko explained, following Shinji's eyes to the collar. "So I got her before any of their damn brats did, so they could use her knowledge to pass exams. Hold out your arms," she told Shinji, before going back to shifting the cord and rattling off letters and numbers.
"He's going to be a cupbearer," Kaji said, "So the full kit, outfits for all of the ceremonies to match the Master's. Except the cupbearer regalia are all designed for a fallen angel, and you'll need to show off the collar, whenever Tabris fits him with one."
"And his coloring's different. Do you have anything else obvious to contribute?" Ritsuko said, rolling her eyes down at the ground instead of up at the heavens.
"Don't make them too much like a regular familiar's," Kaji cautioned her. "We can remove a little fabric later, but I don't think the Master would give a fallen angel's post to someone he didn't want treated with respect. If he ever decided to do something else with Shinji," Shinji wondered what that 'something else' might be, "it'll belong to a fallen angel again. You know what happens to anyone who dares to treat any of them like a familiar they can command." Seeing Shinji's look of not so much curiosity, but need for any information he could absorb, Kaji explained, "One of the inner circle lost a second son that way. The Master doesn't want any of the old men thinking that the fallen angels are just foreign princes they can swindle out of money, power and peasants." Because they would think that way, given half a chance. "So, bringing your mother back to life, right?"
Shinji looked down at his feet. "I'm not really any kind of noble person. I was just afraid of what my Father would do to me."
"When you're father's Gendo Ikari, that's called being sane, kid," Kaji said, ruffling his hair. "All the proper clothes for a young gentleman to wear about the house and about town, so that they'll be there if Master Tabris ever wants them, but I don't think we're going to need riding clothes any time soon, or hunting," he told Maya, who nodded and made a note as Ritsuko pulled up one of Shinji's feet. Shinji had to grab Kaji to keep his balance. "What do you do for fun?" he asked.
"I was told that I should play music, the cello and piano," Shinji told him. "And I was going to ask if Hikari wanted any help in the kitchen?" Did Kaji think that was a good idea. "Or would Ta-Master be upset that I'm doing servant's work?" if he wasn't quite a servant.
"He'll only care if any of the Circle find out and disrespect you for it," Kaji said, clapping Shinji on the back once it was safe for Shinji to let go of him. Once again, Shinji had to flail his arms and try not to fall over. "But he'll discipline them, not you. Master Tabris is fond of his pets, since most of you are future demons. I think the manor's a little like a nursery to him. He'll be pleased that you're playing nice with the others."
Shinji let out a sigh of relief.
"So, did you have any friends back home, a cute little thing like you?" Kaji asked him, since he'd answered Shinji's question.
"Not really. My father didn't want any of the servants to be familiar. At boarding school there was Kensuke, Kensuke Aida, but I don't know what happened to him," Shinji said, staring down at his feet, because worrying about Kensuke was enough that he couldn't really care that Ritsuko's hands were on his behind now.
"Kensuke Aida," Kaji mused aloud. "I'll look into that." Seeing Shinji light up, so surprised, eyes bright with gratitude, he chuckled. "If that's how you respond when someone says they'll do you a favor, the Master's going to have fun spoiling you." Shinji got his hair ruffled again, and he found himself smelling Kaji's cologne, what he thought might be the scent of a man.
Was he already having impure thoughts like that?! He'd always dreaded it before, and now?
"Heh," Kaji said into his ear. "Even Maya thinks you're a cute little thing."
Shinji jumped, and turned to see Kaji grinning at him.
Ritsuko finally let go of him to go back to the desk piled with bottles and tubing, a complicated apparatus. "Drink this," she ordered him.
He swallowed, but the golden liquid didn't look bad, just the color of wheat. It couldn't be beer, but who knew what some strange alchemic potion would do to him? He still drank, though, because he didn't think refusing Ritsuko was an option.
She watched him for a second, frowned, then took out a pocketwatch. "I already tested that batch."
"Well," Kaji said, after tapping Shinji's chest, "the most reasonable explanation is that the kid's blessing included some kind of protection against alchemy. Or at least against shapeshifting. Did Tabris say anything about that?" he asked Shinji.
"I, I said I'd like it if I could look human," Shinji said, looking down at his feet and blushing harder to see what was in the way.
"And that includes being turned into a woman," Ritsuko said disgustedly.
Kaji laughed. "All of us humans are pathetic to the Master, Ritsuko. It's probably just a blanket ward against being shapeshifted. The body belongs to the Master, after all, and he wouldn't want someone tampering with his property. Not when he's such a cute little thing already," Kaji said with a wink at Shinji.
"Will Mistress Ritsuko get in trouble for attempting to change Master Shinji?" Maya looked pale.
Kaji and Ritsuko glanced at each other. "If it was one of the Circle, definitely," Kaji said with utter seriousness, looking first at Maya and then at Shinji: this was something he needed to know too. "The Master will generally accept pleas for forgiveness. Just never, ever make the mistake of thinking it's better to beg forgiveness than ask permission, or assume that he'll forgive you for doing what you wanted to do. That's disrespect, and he won't tolerate it, but," Kaji said, smiling now. "He knows that humans are sinners, incapable of self-control. He's not going to punish us too much for the weakness that makes us fail to live righteous lives and be willing to sell our souls to him in the first place. If humans weren't weak creatures, he'd still be imprisoned in the ice beneath the rest of the world. The good thing about all the ways people mess up is that if we didn't trip ourselves up, fewer of us would fall into his hands, ripe for the plucking. Just look at the Inner Circle. All the power in the world, and if they hadn't wanted more, they would have thought better of something that meant moving up the day the world ends. Tabris has already made it clear he's not interested in letting them take it with them."
"Once we die we'll, he'll… We'll be in hell," Shinji said. "So it's not that efficient to punish us now, when any minor trouble we cause him… We'll be suffering for it later." He knew it was true, that was how demons, no, how the world worked."
A large, strong hand on his shoulder, and "Regretting it?" asked Kaji.
Shinji shook his head. "I'm worthless, and a coward, and… My mother was a lot better person than I am."
Ritsuko snorted, but didn't elaborate.
They kept measuring him, and then holding pieces of cloth up to him, by themselves or in combination, until a small young girl-cat came and summoned Shinji to attend his Master in the bath. Instead of just washing him, Shinji was allowed to get in himself, and all the heat made it easy to relax, or easier than it would have been without it when Tabris put his hand over Shinji's, covering his with it the way he must intend to cover Shinji's body with his own, so Shinji should make the first move and try to see if he could perform his duties some way that wouldn't hurt, or who knew what the devil would decide to do?