I want to take a quick(ish) look at Zeref and Mavis.
In my opinion, these two are the most tragic pair in the entire series. Arguments could be made about Erza and Jellal, or maybe Ultear and Ur but it really is these two. A cursed boy and a cursed girl.
To start, Zeref's entire family was killed, including his baby brother who would have been 7 years old-max. So, as any aspiring wizard does, Zeref started to try and ring Natsu back to life. Some attempts were misguided, like the R-System, but if the Eclipse Gate was worked properly nobody would have to die.
Then, Zeref was kicked out of his school. For the simple act of wanting to see his brother again. And suddenly, he was cursed with the Curse of Contradiction. As a reminder, the curse makes it so the more you value life, the more death magic you emit. Forcing you to either be numb to all life around you (including people, animals, plants etc.) and living in solitude, or loving life and killing everyone you love. And, to top it all off, it makes the cursed immortal. So you are doomed to an entire life of misery, solitude, and death.
So, Zeref moves on trying to ressurect his brother. The worst has already happened to him, so he continues trying. When he finally succeeds, he still has to wait around 400 years to meet his brother again, with the prayer that Natsu would be strong enough to kill him. In that meantime, he doesn't do much, until 300 years into his solitude, when he finds Mavis.
For her part, Mavis was orphaned before the age of 6, and forced into servitude to pay off her parent's debts. Then, everyone she knows except one girl her age, are murdered. She lived for 7 years with that one friend before finally leaving Tenrou Island. Once she does, she a)makes friends, b) learns magic, c) saves a town from an invasion, d) becomes immortal, e) learns her only friend that she had on Tenrou was an illusion her subconscious created to keep her sane and f) gets cursed with that same curse that Zeref has, all within 90 days. But she doesn't realize she is cursed. 10 years later, when she meets Zeref again, he tells her she has the Curse of Contradiction. The crime that she committed to get this curse? Saving a friends life.
Of course she doesn't believe him, and goes back to the guild she founded and witnesses the birth of Makarov. Then, as one does, she is hit by a wave of appreciation for life. That activates the curse, and then Makarov's mother died.
Mavis took off, wandering around for a year including starving herself for 6 months before Zeref finds her. Realizing that they are the only two people who can love each other, they kiss. Zeref, being cursed for far longer, feels actual love for her. She, seeing a soul that needs love desperately, feels compassionate for him. Compassion not quite equaling love, he kills her.
Then, in probably the truest act of love in the story, Zeref returned Mavis’ body to the guild, to people that love her. To do that, he had to stop loving her. That moment hurt me on a fundamental level.
To top it all off, Mavis and Zeref have a kid. The kid knows that Zeref is his father, but also knows about the curse. So he can’t tell Zeref the truth. Which would be worse? Telling Zeref that he is Augusts father and being killed by the curse, or learning that your own father didn’t truly love you? I haven’t quite gotten to the part where August dies yet but it is going to be awful.
And the only way to save the world from Zeref taking it over?? It’s simple. Mavis figured it out from watching Natsu and Lucy fight together. She just had to love him. This sent both of them to their final deaths. The one magic, love.
