Disclaimer: I am not J. K. Rowling. No profit is made. Don't sue! I'm poor.
A/N This will be the basis for later actions.
Gilligan was bored. In all his years the lake had never changed. After all, he was just a squidling when the school was built. He had seen many people come and go, from his view under the lake, and for whatever reason many people came in pairs to a tree by the shore. He never heard what they said but he assumed it was some type of mating ritual. He thought humans were strange, and also wondered why did they always brought bread? He ate fish, so why didn't they bring some meat to appease the mighty squid lord master of all. Gilligan realized he had digressed.
Many people visited him, but certain pairs seemed to come far more frequently then the rest. The first was the only pair that actually stopped to chat with him. When he was a young squidling two humans could speak to him strangely enough. They had very strange names, Godric and Salazar. Gilligan laughed at them for a moment. But yes, they weren't actually mating though. They said they were friends. Gilligan was always skeptical, but he never pressed the matter too hard. One day whilst chatting with Godric, Gilligan saw Salazar rushing out of the castle. He watched as Godric raced over to his friend. Salazar shoved him and disappeared. Godric returned in strange spirits. Gilligan inquired and learned that the two female leaders were apparently mating and Salazar had entered their chambers. Gilligan didn't understand then, nor did he understand now. Apart from a useless mating, why would Salazar be rushed to leave? Gilligan asked this and was told that it was also the place they had chosen to mate a room that humans called the kitchens. He then learned that's where they prepared food.
The next pair of note was one Gilligan had watched for many years; a young teacher and a student. He thought here was a mating of power. A strong male and female whose offspring would be strong indeed. The male must be strong to reach the position of power he held, he was a teacher; and the female was powerful to have attracted his notice. However he never saw the couple produce any offspring. As the man's robe grew more purple and she grew aged, he began to think that any offspring would have been born without the desire to mate and thus lost the useful power. He shrugged his tentacles and continued his lazy circuit of his lake.
You see having been there so many years, despite what the merpeople and grindylows liked to think, he controlled the lake. They bowed to him. And brought him fish as tribute. He continued swimming.
The next pair was a more recent appearance a blond boy and dark haired boy. Once again Gilligan thought it was a useless mating. After all how would they produce any offspring? Furthermore they seemed to only spend time at his lake, and he was getting tired of it. He slapped the water with a tentacle as a warning to leave. They were either very brave or stupid because they didn't move. And they continued to return for three years. Gilligan wished that he had killed the dark haired one when he was foolish enough to jump into the lake. But that was before the relationship started.
Another pair was also rather recent, and red haired male, and some brown haired female. The female was exceedingly loud; her mating cries pierced even the barrier of his lake. He wondered if the female was blind because she was so loud when a potential mate was so close. If so she would be a terrible choice for a mate, after all mating with a deformed creature would make for weak offspring. Gilligan shrugged his tentacles and continued his swim.