Sibling Love
They weren't strictly brothers. No, they were, as the humans called it, half-brothers. Their mother, the white and silver Windsign, had been a meteorologist back on Cybertron.
First, he had come. His father was a red and indigo security mech, Base Support. Until that fateful day, when he was 3.2 vorns old. He remembered it well.
"Yes, I will tell the lad," she had sighed into the comm, distress in her voice. She beckoned him to the couch.
"Mother," he asked as he sat down., a hint of worry in his voice, "What's going on?"
"Red… your father… he's gone." Pure and simple. "A crazy mech launched a raid on the outpost. Base… was the first causalty."
The next thing he remembered was quietly beginning to sob into her shoulder, her sobbing alongside him.
A vorn later, he had joined the Autobot militia as a security officer and was working when Windsign commed him. She had bonded with a government packer named Pack-In. Together they had had a rare set of twins, one sparkling scarlet, the other gold.
Sideswipe and Sunstreaker.
At first he was infuriated, angry that his mother had betrayed his father. When he met the twins, however, his world changed.
They treated his paranoia with respect, respected his father, and overall genuinely wanted to be friends with him. As he watched them grow in the Autobot army, he noticed that he was the only one they did this to, pranking or beating on everyone else.
That didn't mean he didn't get pranked. No, to uphold sibling rivalry, in public, they tortured him the worst. But, in private, they always apologized. He had trained them in combat alertness, mourned with them at their mother's funeral, and been there whenever they were hurt.
He didn't like to acknowledge it, but he was closer to them than anyone else, despite how much hell they inflicted on each other.
Now as he lay in his berth, held down by the mass that was Wheeljack's latest creation (the Heavy-whatinator gun or something), Red Alert remembered that he was pranked more often than even Prowl because, after all, sibling rivalry, sibling love.