Ritsuka had become an orphan from the previous Holy Grail War. With so much collateral damage and lives lost, there were those left with no place to go. Many Servants had remained in the world long after the fighting ended, summoned into being by the Chaldea Organization. One of them was Minamoto no Yorimitsu, more commonly known as Raikou. Left in the modern world without someone to live with her, she was overcome with motherly instincts.
It had started simple. Living in her place by herself, she made plenty of food. Expecting to have a husband and a son to share her motherly life with, she made servings for three people. All sorts of traditional dishes, including huge bowls of rice. However, there weren’t three people living in the apartment. There was only one. So she ate all of the servings herself, not stopping until the plates were empty and sauce was dribbling down her chin.
Raikou let out a burp and looked down at the front of her body. Her boobs were already the biggest among the various Servants in the modern world, and her belly was starting to pack on the pounds. It had already become round and slovenly, looking like a small beanbag chair in the middle of her body. Yet when she looked down at it, she felt a sense of happiness.
“I’m getting fat...” she said. “It makes me look like a mother. If only there was a baby in this belly. I love my food baby, but... I need more.”
In time, she found out a young man named Ritsuka Fujimaru was looking to be adopted. He was a young man of average looks, with spiky black hair, looking for a direction in life. Out of the kindness of her heart, Raikou adopted him. The paperwork was confusing, since her birthdate was several centuries in the past, but Chaldea made sure that everything was taken care of.
A short while later, Ritsuka came to live in her apartment. She welcomed him inside, and couldn’t help but notice a bulge in his pants that had sprung up when she wasn’t looking. “Did he get hard when he saw his adoptive mother?” Raikou thought. She noticed that her shirt wasn’t pulling down all the way, showing her pudgy belly and the underside of her boobs. She had made the boy who was to be her son horny on the first day they met. “I’m a failure as a mother,” she thought. “But I’ll make the best of this.”
Knowing she had one more person in the house, that night Raikou made four portions of food. She was stuck in her old habits, and ended up making more than the two of them could eat. After Ritsuka had finished his meal, he stared in awe as Raikou continued eating all the extra food she had made. Grilled meats and fish and all sorts of traditional dishes were eaten, never skipping a beat. He watched as Raikou’s pudgy belly began to squish into the table, pushing her away in her chair.
“Wow. You can eat a lot,” said Ritsuka.
“I keep meaning to have people to share it with,” said Raikou, ending her sentence with a burp, “but I’ve never had anyone until now. Tell me, Ritsuka. What do you think of having sex with someone who’s related to you? But not by blood?”
“Why are you asking?” he questioned.
“I’ve felt your hot stares. On my breasts and my ass. And my belly,” said Raikou. “I know I gain weight easily, but you don’t think I’m unattractive, do you?’
“Of course not. Your body is very voluptuous... and sexy...” said Ritsuka.
“So you admit your mother’s body is making you hard?” asked Raikou. “Prove it to me! Show me your penis!”
Ritsuka stood up from the table and lowered his pants and boxers. His cock was springing forward, bouncing joyfully at the sight of Raikou’s food-stuffed, exposed belly. Raikou saw his glans was already dripping with precum, and his balls looked stuffed full of thick, virile young sperm. She had noticed what was probably semen stains from him masturbating with her underwear, and could recognize the smell. They had only known each other for about a month, and there was no doubt.
This boy wanted to fuck her.
“He’s so much younger than me... but I want that cock,” said Raikou. “Ritsuka, your mother is feeling horny. Can you soothe her aching pussy with your throbbing meat-rod? It’d mean the world to me.”
Raikou stripped down to her underwear. Her massive breasts were just barely restrained by her purple lace bra, and her chubby ass cheeks were hanging through the sides of her underwear. She had a prominent set of love handles that emphasized her belly, though her combat skills had not atrophied in the meantime. Perhaps it was something to do with the magic that had summoned her here.
She was a tall woman, approaching six feet, and so the tip of Ritsuka’s dick pushed up against her body, sinking into her belly button. He reached around and grabbed her oversized ass, his dick starting to rub in her stomach. The squishy folds of Raikou’s stomach closed around his shaft. Raikou could feel his hot dick throbbing against her skin. She loved this sensation, but she wanted to have that magnificent young cock inside her right now. Panting as if in heat, she called out to him.
“I’m so fucking wet. Take off my panties, please!” she said.
Raikou unhooked her bra as Ritsuka lowered her panties. Her sweater and shorts were on the floor alongside her underwear, leaving her standing naked in front of her adopted son. When Ritsuka pulled down her panties, he saw lines of love juice trail from her pussy down to the stain in her underwear. Her pussy was covered in a dark purple pubic hair. There was no doubt that Raikou had the bush of a mature woman. To say nothing of her breasts. Her fantastic breasts were the largest he’d ever seen, with a cup size that was usually only seen in AV sites. Her nipples were a shade of light brown, standing firm and erect on top of the massive white mounds of her chest, enticing him to come enjoy her body.
“Miss Raikou, you’re beautiful,” she said. “You’re so voluptuous. Especially your belly. I’ve loved it since the first day I saw you.”
“I knew you liked me in that way,” said Raikou. “Tell me, Ritsuka. There’s one way to make a woman’s belly bigger that only a man can do. Do you know what it is?”
“Getting her pregnant?” asked Ritsuka.
“Exactly,” said Raikou. “I’ve always wanted to be a mother, and I think your cock is the one to do it. I don’t care if you’re my adopted son. As long as there’s love between us, we should start mating like animals, right here. Look at how wet I am. Come, stick that hard thing in me already.”
Though Ritsuka didn’t know it, Raikou had been putting special Onigashima herbs in his food. They were known for increasing virility, including vastly multiplying the amount of semen a man could release in one burst. Raikou had been wanting him to impregnate her for some time. Everything had been leading up to this moment. Raikou bent over on the counter, spreading her chubby ass and showing her pussy, drops of love juice falling to the floor.
“Mom... I’m putting it in,” said Ritsuka.
“That’s my boy,” said Raikou.
Raikou’s wet pussy swallowed up his cockhead, followed quickly by the rest. Her warm folds wrapped around him, squeezing in on the sides of his cock. Ritsuka wrapped his hands around her body, grabbing onto her belly and rubbing it. He could still feel all the food she had eaten sloshing around in there. Raikou moaned as his warm hands touched her stomach, the feeling of his hands and dick attacking her body from both angles.
“You’re so thick,” Raikou said. “It’s even better than I imagined.”
“I love how soft your belly is,” said Ritsuka. “And your ass is so fat.”
“A mother needs to have good breeding hips, if she’s going to give birth to your babies,” said Raikou. “You can play with my butt too, if you want.”
Ritsuka reached down and slapped Raikou’s ass. Her butt flesh jiggled in response to his touch, shaking at the same time as her tits. Her dangling boobs swayed back and forth as Raikou pushed in and out of her, thrusting into her pussy with even greater intensity. It was so tight that she wasn’t going to let him go. Ritsuka reached upward and grabbed Raikou’s boobs, massaging the fat tips in his hand. Her hard nipples only made her moans louder, and her pussy continued to tighten around him.
“My nipples... my belly... I can’t hold on any longer! I’m gonna cum!” said Raikou. “I don’t want to cum until I have your seed in me! Please, fill my womb with your cum!”
“I... can’t hold on much longer either,” said Ritsuka. “I’m going to...”
Ritsuka came. A hot, steady flow of cum from his balls pumped into Raikou’s pussy. She let out a heavy sigh that was nearly a moan as she felt that wave of hot, sticky cum she had been waiting for begin to enter her pussy. She had asked him on a day when she knew she was ovulating, so that it was almost certain she would get pregnant. Even knowing what effect the herbs had, she wasn’t expecting this much cum.
Her pussy was immediately filled up, and began to overflow with the sticky, white goo. It ran down her legs and onto the floor, yet Ritsuka’s cock remained hard. It just kept going. Raikou looked beyond her cleavage towards her belly, which was continuing to expand as more and more cum entered her womb. Her belly, already stuffed from her three portions of dinner, was expanding to where Ritsuka, still trapped by the tight grip of her pussy, was being pushed back.
“This is... so... good...” said Raikou. “I’m full of cum! My son’s thick, sticky cum! I’ve never been so happy to be a mom!”
“Why am I doing this?” asked Ritsuka. “This much never came out when I masturbated before.”
“Perhaps... it’s a mother’s love,” said Raikou.
After what felt like a full minute, Ritsuka finally stopped cumming. He pulled out of Raikou, who had slumped to the floor. She was stroking her cum-swollen belly, basking in the warmth of her son’s semen flowing from her womb to her feet. If she tried to put on her panties or her shorts, there was no way they would fit anymore. Her belly was too big to contain them. It had swollen to the size of a fully inflated beach ball, with her belly button being the valve.
“When will this go down?” asked Ritsuka.
“Once I’ve been fertilized,” said Raikou. “We’re going to have so many children. Thanks for knocking me up. Your mother’s proud of you.”
Ritsuka, exhausted from cumming that much for the first time in his life, walked over to his adopted mother and rested his head on her belly. He could feel the warmth. Her belly was soft, full of cum and food and so much fat that had built up. Though both of them were sweaty and sticky from sex, they thought it would be okay if they fell asleep right there in the kitchen. It was the start of a new chapter of their lives, for both of them.