Onii-chan~

As the three of you walk, Illya explains your connection with her through your adoptive father, Kiritsugu Emiya. She goes on to elaborate how much she hated the man for essentially abandoning her and her mother during the 4th holy grail war. "You know, I wanted to kill you for a long time. But then, I realized I was being my Grandfather's pawn. So I changed the summoning ritual to summon Berserker and instead summoned Rider." She says. You don't say anything as Illya struggles to get out the next bits. "He didn't take to that too well. I decided then to love you like a sister should. Thankfully Rider let me escape. I tried to find you so we could support you but Lancer found us first, and well, you know the rest."

The three of you arrive at the Emyia residence to find it empty. Rin has apparently sauntered off to do her own thing for a while, leaving the house in a state of rare silence. "I guess this will do." Illya says as she crosses the threshold of your doorway and removes her shoes. Caster looks at her with a smirk. "Yes, I imagine you growing up in a huge castle makes you fit to ridicule my beloved husband's home. His home is my home, and I am happy to be here with him, in this place even though my own domain is much more opulent than that of your own.

Caster leads you along to your bedroom door and opens it. It reveals your futon and place of rest, of course. "Come." Caster says as the both of you step foot into the doorway whiy acts as the gateway into Caster's domain. Illya watches as you step foot into an otherwise normal bedroom, only to vanish from sight. "Neat trick." She chides before following suit.

The trio of you arrive in Caster's bedroom as always and appear on the balcony overlooking the huge temple grounds and other various buildings. Illya's jaw drops as she enters Caster's gigantic domain. "Woah." She says. "Yeah, Caster's pretty great." You say. "You have no place to speak of my husband's home, when I have this as my comparison. I prefer his warm, comfortable home with being in his arms over the beauty of my vast land."

Caster leads you to a set of chairs that have been set on the balcony. You sit down first as Caster finishes scolding Illya, "Now, I believe you owe my husband an apology." Illya nods, "Sorry I was not appreciative of your home. Please let me make it up to you for both my words and for saving me from Lancer."

You are about to speak when your lips were summarily interrupted by Illya's own as she misses you firmly and slips into your lap, face first. Your eyes open with surprise as her lithe legs around your waist. It seems, you have little voice but to accept this girl's attention, like it or not. As she showers your lips with kisses (to allow you room to breathe in-between more passionate kissing), she grabs your hands and places them on her hiked up skirt.

You nervously look over to Caster who just shrugs her shoulders. She silently mouths you to enjoy it, so you close your eyes and finally begin to reciprocate Illya's attention. The lewd sounds of your wild kissing echo off the temple grounds as Illya hugs you tightly, happy that you are finally an active participant in this ride. Speaking of ride, you feel a soft hand grasp your cock for a moment before feeling the unmistakable heat of your shaft rubbing against Illya.

With a push of her hips, you are unmistakably and irrevocably inside this 18 year old girl as she hilts your bare cock fully inside her sticky, sweet honey hole even though she's otherwise fully dressed. "Onii-chan~" Illya moans. You slip your hands up her legs and skirt to caress and grasp her ass as she rides your cock. Nothing is said between you two as you let your love-making speak for itself. With a grip of her tight pussy, you erupt deep inside your very sister's babymaker and tense up at the throes of your own orgasm as well as her own.