If a lore buff is reading this is it at;east possible that giants are related to mer? You see I was playing Skyrim. I saw a giant in a loading screen. And I noticed he/she has pointy ears... So I am wondering..

That would be quite interesting, and we know that the Dwemer had dealings with them, but I can't recall anything suggesting a connection. As for pointed ears, there are a number of other critters with pointed ears in Tamriel and I don't imagine they're all related to elves.

But is there a theory suggesting that they are related once?

Well, I assume lore wise that they have black souls (not in-game) which means they probably have the same ancestors.

After all, humans and Tsaescii are related to Elves.

There are creatures with pointed ears other than elves. Although I will go ahead and try to make a connection between the giants & elves.

Well a starting point might be to relate the ogres to the giants, both of them have extended brows, pointed ears, live out nomadic existences,
they both also resemble civilised counterparts: nords and orcs. My own belief is that ogres and giants are simply orsimer/nords heavily affected
by the curse of Malacath that they transformed to become more alike in their existence to the Daedric Prince's sphere.

Giants are the forefathers of the Nords before they got shorter. It was also them who named the Dwemer 'Dwarves'.

There's more to imply that the Giants are related to men, actually.

What if giants are the closest link to the Ehlnofey? This explains their Nordic facial features and their ears.

Fascinating stuff