These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
When Marcos learns that Héctor is actually his uncle, the two share one of this.
Iván and Julia's reconciliation after Iván broke up with her so that she wouldn't have to take care of him since he has Alzheimer.
When, after more than 30 years of separation, Héctor finally meets with his sister Sandra.
Draco in Leather Pants: one of the greatest examples is Hugo, who was shown to be a very bad person practically from the first episode he appeared in, yet he has been regarded as one of the most attractive guys in the series.
Jacques Noiret is also a good example. He was cruel to his son and to Elsa when she was his girlfriend, but several girls and women like him. His eleventh-hour Heel-Face Turn didn't help matters.
Nicolás Garrido became this quite soon: he was quite a Jerkass at the start, yet everyone was hoping that he came into the school and hooked up with Elsa. Even after discovering he was into the plan to kill everyone inside the school people still liked him.
Ensemble Darkhorse: Fermín, the school's cook, who was only intended to be a background character at the start of the series, but when he started to gain popularity he was turned into a spy that had been sent into the school to discover the Big Bad's plans, as well as finding many objects that had been stolen from Jewish people during World War II.
Julia, entering the school in the 2nd season, was nearly from the start a popular character with her attitude and very happy disposition.
Fridge Brilliance: in the last episode, Héctor asks about Elsa - who had been his girlfriend of years and wife for a few months, but whom he had broken up with after learning she had cheaten on him with his best friend - but doesn't say a thing about Lucía - who had been his girlfriend for the last months before the summer. Many fans wondered why, but then the brilliance struck: since he was hidden in the basements and Lucía would have been in charge of his healing, then he would have realised that she was part of the bad guys.
He's Just Hiding: when Héctor died, many fans thought that he was still alive and his death was only simulated. They were right.
Also thought about Carol, because few could believe that her character, one of the favourites of the audience, would actually die. This time, they were wrong.
In-universe example: the bad guys were Nazis and had simulated their deaths in the past to avoid being caught.
Moral Event Horizon: Jacques Noiret happily letting Iván getting infected with The Virus so that he doesn't interfere in his plans and blackmailing him so that he tells him where María is.
Roque reaches this when he hits Carol and makes her fall down a very tall tower, then burying her instead of checking whether she is alive. When he later gets a call from her mobile phone he doesn't tell the others, he distracts his friends so that he can reach Carol first and when he finds her the only reason he doesn't kill her is because Marcos arrives there on time. Not that it was soon enough to prevent her death.
Ritter Wulf when he created The Virus and started to experiment on the prisoners of the Belzec extermination camp.
Nausea Fuel: when Héctor discovers the corpses of his old orphanage friends in the middle of the forest.
The "home videos" with the experiments on the orphans back in the 50s-70s (also qualify as Nightmare Fuel).
Also Paula's eyes when they suddenly start to emit light in the middle of the night.
Julia's encounters with the ghosts are this for her. The creepiest one is when she meets Eva's ghost... at the same moment Paula passes near the ghost.
Shipping: almost from the start, people wanted Marcos and Carol to hook up. It would take nearly 5 seasons for that to happen. And then Carol died.
Iván and Julia would become one of the fans' favourite couples.
Starting with the 3rd season, many fans were divided between those that wanted Marcos and Carol to be together and those that wanted him to be with Amelia. Even after knowing that Amelia was part of the bad guys. Amaia in the 6th and 7th season would also become a part of this war. In the moment she was revealed to be the grand-daughter of one of the bad guys and The Mole, everything changed.
Too Cool to Live: Fermín. He certainly was the biggest Bad Ass of the series, the greatest hero... and he gets stabbed by Garrido in the last episode, dying in María's embrace.