Gavin is right to be annoyed, given that it's his little brother, Lewis that is getting bullied by boys who are a year older than him, so his mind was always trying to break off and teach them a lesson. But as he was storming through the park, something was different with him, but he somehow doesn't even notice just as he had his eyes on them.
As it happens, he was starting to get bigger and fatter, as if he's adding loads of massive and blubber instantly. His belly had expanded so much that it ended up spilled over his sweatpants, and that caused his t-shirt to ride up that was getting so tight, just to see his fat belly jiggling, while his shirt is pushed out by his moobs that are getting bigger.
Every part of his body are getting thicker, including his arms, and legs, but the biggest feature to grow massively are his butt and thighs, and that he was getting a bottom-heavy shaped body. It was so huge that it caused it to jiggle violently that it would've made people stare in awe to see his fat booty waddling past. So much that he continued to grow fatter so suddenly, until he was up to half-a-ton, and yet he still hadn't noticed anything different, when his focus was stopping these bullies from beating up Lewis.
When Gavin did manage to get to them, two of the bullies, who were holding Lewis by his arms each, were left in stunned and let's him go, though he was kinda beat up at this stage, and thus unaware who this big, massive guy is until he heard his voice, when sitting up, saw him confront the main 10 year old bully named, Ricky.
"Hey, you better leave my little brother alone, or else?" Gavin warned the bullies by placing his hands on his wider hips.
"G-Gavin?!!!" That was when Lewis realised who this fatter guy is, as he never thought of seeing a massive, bottom-shaped girth quite like it, especially when he says in his own thoughts about it. "He's so big! How did he grew so much fatter?"
While Lewis was in complete surprise and the two bullies actually backing themselves out, it did not phase Ricky, as all he could do is stand there and chuckle, before he gave it a slap on Gavin's fat belly that was so soft, and caused to jiggle.
"Is that so, fatty?" Ricky laughed at Gavin, not knowing that he was still gonna teach the bully a lesson. "What are you gonna do..."