One reason could be overeating. Just like in the story of the forest monster that ate too many magic fruits. Another reason might be a change in its environment that led to more accessible food sources. For example, the water monster had more nutritious plankton available due to the fairies' spell.
Once upon a time, there was a water - dwelling monster. It used to be very slender and agile. However, a group of kind - hearted fairies thought it was too thin and needed more energy. So they cast a spell on the river where the monster lived. The water became filled with a special kind of plankton that was extremely nutritious. The monster ate so much of it that it soon started to gain weight. Its scales became tighter as its body grew bigger, and it had to learn to move more slowly in the water.
Once there was a mermaid monster girl. She lived in a peaceful underwater kingdom. But then she discovered a magical seaweed that was extremely delicious. She couldn't resist eating it every day. As a result, she started to gain weight. Her once slender tail became plumper and she had a bit of a belly. But this new look made her unique among the other mermaids, and she learned to embrace her new body and the confidence it brought.
One possible theme could be body acceptance. If the monster girls gain weight, they may have to come to terms with their new bodies and learn to love themselves regardless of their appearance.
I don't know the exact details of 'Monster Musume Weight Gain Story'. However, if it's like other similar stories, it may focus on the journey of the monster girls in the story. Maybe some of them gain weight unexpectedly and have to deal with the consequences. It could be about their struggle to adapt to the new physical state, how their friends react, and what they do to either accept it or try to change it back.
Perhaps an older, veteran hunter. After years of successful hunts, they start to relax a bit. They become less strict with their diet and start to gain weight. This weight gain makes them re - evaluate their hunting skills and they have to find new ways to be effective in the field again.
One possible plot could be a hunter who, after a series of successful hunts, starts to overindulge in the feasts held in the village to celebrate. They keep eating rich, fatty meats and large amounts of ale. As a result, they gradually gain weight. This added weight initially affects their mobility during hunts, making them slower and less agile. But then, they start to adapt their hunting style, using their newfound strength from the extra weight to their advantage, like being able to withstand stronger monster attacks or being able to use heavier weapons more effectively.
One reason could be overeating. Just like in the case of the cat - eared monster girl in the bakery. The delicious food was too tempting, so she ate more than she should, leading to weight gain.
My best weight gain story was when I started lifting weights. I was really skinny before. I ate a lot of protein-rich foods like chicken and eggs, and combined it with regular strength training. In just a few months, I saw significant changes. I gained muscle mass and my clothes started to fit tighter in a good way. It not only changed my physique but also boosted my confidence.
Increasing your physical activity is crucial. Try to find ways to exercise even in a home environment. You could go for a jog around the neighborhood in the morning or do some bodyweight exercises in your room like push - ups and sit - ups. Also, if possible, take the stairs instead of the elevator. Another important thing is to establish a regular routine again. Go to bed and wake up at the same time every day to get your metabolism back on track.