If you read Bleach, you'll find an old friend in here....
"Archer. You may materialize." Rin stood in an out-of-the-way alley, carrying a bundle.
The ever-present Servant appeared smoothly into the realm of human sight. "Yes?"
"Wear these. We're going shopping." Rin held out the bundle to him, dropped it into an incredulous hand, and started striding out of the alley.
"What?" Archer was still frozen there, amazed by the audacity of his Master.
"You heard me; we're going shopping. I have needs too, Archer, don't look so surprised. And I can't exactly have you walking around wearing your armor in public. Just put them on over your armor. Unless you have attire other than battle gear?" Still shocked, Archer began to mechanically follow her orders, vanishing the coat, and pulling on a sweat shirt and jeans.
"Where exactly are we going, Master?"
"I've been subsisting these past few weeks on tea and sandwiches, and while your tea is quite excellent, I can't survive on it alone. I have dietary needs that need to be met. I also need to buy some other essentials." Rin looked quite unfazed at ordering her Servant to become her manservant as well. Nor did she seem particularly troubled by the fact that Archer wasn't exactly an inconspicuous companion. Archer shrugged and followed her with the air of someone who had given up.
It turned out that "essentials" also entailed a bit of stopover at several jewelry stores and tea houses, as well as a few clothing stores in addition to simple grocery shopping. Granted, the jewelry was to be made into more carriers of mana, and she had quite a discerning taste in teas, but clothing stores? She didn't even buy anything, just walked in, traversed every inch of the floorspace, maybe looked at one or two things, and walked back out. Archer felt he was being deliberately used to make the point that she could make him do whatever she wanted him to do.
"One last stop. It's a jewelry store known for diamonds, and I used my last one on Shirou." They entered the store and were immediately greeted by one of the counter clerks.
"Ah, Rin-san. What can I get you today? Who's this? Your boyfriend?" A man in his mid-forties or fifties put down the emerald he was wiping down and came over to them. He was wearing a kimono and geta, and his eyes and sandy hair were half obscured by a green and white striped hat. Archer eyed him neutrally, not sure whether he approved or not of his master patronizing such a shady looking character.
"Good afternoon, Kisuke-san. I'm looking for some diamonds—small, less than one carat, maybe about ten to twenty points. And no, this is not my boyfriend, merely a new Servant." Somehow, this stung a bit with Archer—only a bit, he reminded himself, as he turned to look at the other, extremely varied items for sale. The store permit stated that this stored belonged to an Urahara Kisuke.
"You're in luck; a new shipment of raw diamonds came in, and there are a few chips that were too valuable to go to waste." Kisuke brought out a couple of trays filled with bits of gems too small to stand alone, but could be used to enhance other pieces of jewelry. After a bit of scrutinizing, Rin picked out a few of the finely cut chips and made her way to the register. Archer waited patiently, looking through the stacks of magazines, but not really concentrating on what he was picking up and putting back down.
As he rang up the sale, Rin looked around the shop. Her eyes were caught by a small ring that sparkled on the shelf behind Kisuke.
"Wait a moment. May I see that?"
"Ah yes, this ring?" Upon closer inspection, it proved to be merely a cleverly shaped ring of sterling silver, with notches and small facets cut into it to make it seem as though it had gems shining out of it.
"I would like one." She showed him two fingers. Kisuke nodded, immediately understanding what she meant, and wrapped up the box for her and rang it up as well.
"Archer, let's go." Startled, Archer realized he was holding an ero magazine and Rin was looking at him somewhat quizzically.
Once at home, Archer quickly removed the sweatshirt and jeans and put his coat back on. The little stunt she'd pulled hadn't been a disaster, but really, he shouldn't be visible to the general public.
"What was the purpose of that trip?"
"You bought nothing but tea and gemstones."
"I bought food too, and a present for myself." Rin smiled like a vixen. "Archer, make some tea after I'm done with my bath. I'll put away the groceries." Archer complied, and disappeared once more. Rin cleared away the result of the day's shopping, leaving the desired tea on the counter, and then headed upstairs for her bath.
As Rin relaxed in her bath, Archer rematerialized in the kitchen, opened the tin of tea, and nearly started at what he saw in the tin. Then he calmed down and busied himself with the tea.
He served the tea to her in the study, where she sat pouring mana into some of her new gemstones.
"Your tea." He took his cup and sat back on the couch. Rin thanked him seemingly absent-mindedly, absorbed by the task at hand, and turned away hiding her smile in her cup.
The rings fit perfectly on their fingers, sparkling just out of sight.