Giant

giants as a group were originally created by Ymir, the various species of giants all are thus related in their origin. Though a lot of the giants have since then either lost their own history forgetting where they come from as a result or see the different giant types as only very distantly related.
There are a LOT of giant species created by Ymir, and even more that Ymir probably personally destroyed. Ymir was a creator. The giants were Ymir trying to mess with reality to create his own species, Ymir could create matter, but it took him many tries to even get a creation that biologically could exist. Eventually he got one, Ymir unlike the other elementals saw potential in the biological soul mix, and when he saw the humans he decided that that as a base was ingenious, that the universe of chance could come up with better ideas that Ymir the thinker ever could. and so running with that concept Ymir went to work, because of this all the giants have their bodies based on humans(and can theoretically have children with them) Giants as a species are biological, but they hold a clear elemental ancestry too, with some of the giants holding magical powers.
the different giant species:

• hecatonchires, one of the first giants created and a failure in ymir’s eyes, for that he locked them away.
• cyclops, the cyclops were also a failure, the next iteration after the hecatonchires, for ymir it was a step better but still not worth having out there.
• Titans were the ultimate creation of Ymir, incredibly powerful yet one of the smallest giants Ymir had created, they all had a lot of souls and could handle them without a lot of issue, only a couple were pushed too far. Ymir however flew too close to the sun with this one and the titans rebelled quite quickly
• ettin, again another 1 of the early creations that went wrong
• ogre, the ogre is one of the experiments leading up to what’s now called the true giants, you can see this continue in the form of the hill giants.
• oni, also called mage giants, were ymir’s attempts to make innately magical ogres. These ogres come in different colors. It seems random as 2 weak ogres are able to birth a stronger ogre, the color makes both their body and magic different.
• troll, another attempt of ymir for certain abilities, this time regenerative, due to their regenerative nature trolls also magically adapt to environments. trolls are actually rightly associated with the fey often, as they often congregate with fey deep in forests too.
• goliath, another of the relatively smaller creations of ymir, these giants are incredibly tough, people think it might have been an attempt to get as close to human creatures as possible, either way these are built like bricks.
• elemental giants, the line of giants were the buildup to creating the titan, they are the main species that didn’t rebel and stayed loyal, in the end these turned out to be the best creation in ymir’s eyes as they were loyal. these giants have been infused with an element during their creation which shows in them. these elements are not the 4 common ones entirely.
• firbolg, the firbolg are the forest giants, ymir made a creature for different environments, hoping that way they could dominate them all. Although other people say the forest giants were made by some other elemental, either way the firbolg went extinct in a lot of places and are now quite rare, they thrive in woodlands best. they aren’t as much associated with giants due to their relatively short height, and more importantly their nature. they take care of the forest having natural magic for it even. The firbolg often have cowlike features, this has nothing to do with their original firbolg nature but instead that quite a lot of them became cow beastman from that beastlord, now it just permeates most communities a bit causing a spread.

Giants being all derived from humans originally causes giants and humanoids to be theoretically able to have children together but, it's a rare occurrence due to both the fact that giants live relatively separate and because of the complications during pregnancy making half-giants very rare to be born. the smaller the giant the less this issue is a thing.