Regulus knew how to swim; he had always been a good swimmer ever since he was little and spent summers with his uncle Alphard. Being in the water was liberating—the smooth sensation of water against his skin, the muffled sounds of the outside world when he submerged his head, and the captivating underwater life fascinated Regulus.
While many people yearned to fly for a sense of freedom, Regulus sought freedom through swimming, immersing himself in a forbidden life that seemed unattainable due to his human condition. He enjoyed opening his eyes underwater and holding his breath for as long as possible, allowing him to momentarily connect with the colorful coral, stingrays, starfish, and, on one fortunate occasion, a shark. It was a magnificent creature, a Carcharhinus leucas, commonly known as a bulldog shark or "requin bouledogue" in French, as he discovered after conducting some research.
When Regulus was sorted into Hogwarts, he chose Slytherin, even though Ravenclaw might have suited him better. His decision was motivated not only by Slytherin's long-standing tradition but also by tales he had heard about the common room being underwater. The mere thought excited him, as it meant he could delve into his research on the species inhabiting the Black Lake every day.
During Regulus's time at Hogwarts, he even invented a way to communicate with the mermaids, beautiful creatures that some found intimidating. They took a liking to him, and occasionally, on summer days when he sat by the lake reading, they would send him shells, each more beautiful than the last.
Every year before summer, after curfew, Regulus would sneak into the lake for a swim. He was never caught, which was for the best, allowing him to relax and forget about everything before returning to his role as the Black family's spare. When he became the heir at the age of fifteen, his visits to the lake became more frequent, even during the winter, as he sought solace and freedom there.
And then he received the Dark Mark—the youngest to bear it—a symbol he should have been proud of. It was what everyone in his family, well, everyone except his brother, would be proud off, but when was his brother please with him? Perhaps his uncle Alphard wouldn't have approved either, but Regulus didn't have to worry for long, as his uncle passed away just a month after he received the mark. Alphard left everything to Sirius and got himself disowned. But he did leave Regulus one thing—the house where he had learned to swim.
Regulus drank the potion, enduring the vile and heart-wrenching experiences it brought, but he knew it was necessary. After finishing the potion and swapping the lockets, he made his way to the water, seeking his freedom, hoping it would alleviate the pain caused by the potion.
As he touched the water, a sense of relief washed over him, but soon hands grabbed him and dragged him deep beneath the surface. The hands tore into his skin, and Regulus was horrified to realize that the very thing that had granted him freedom would now bring his demise. But isn't death also a form of freedom? As Regulus took his final breath, filled with water, he found solace in the fact that he would finally become part of the world he believed to be inaccessible.
Regulus didn't drown—he was too skilled of a swimmer for that.
He was drowned.