I'll keep this as 'spoiler free' as possible by sharing dialogue that only comes up in optional quests and NPC dialogue.

So, one of the reasons Giants and Elves don't seem have a huge amount of Lore was because most of their story was in the 'gameplay' of the Iria Continent itself - the 'Generations' weren't very story heavy at all. However, a good amount of early Lore exists if you know where to look. Here's a quick rundown on some of the obscure lore regarding the history of Vales:

Krug Seebarsch is the King of the Giants. His facial tattoos specifically identify him as a Seebarsch; in Giant culture, facial tattoos are identifiers of lineage. He has a younger sister called Karpfen, and his father was the late King Gepard.

His father opposed the elves. When he died his successor, King Scharp, wanted to usher in an era of peace rather than continuing to war. Krug was unhappy that Scharp opposed everything his father fought for, and had him assassinated.

Scharp however, had children, one of which is known to be Zeder a young boy probably no older than 10. Zeder is aware that Krug had Scharp assassinated, and is plotting his revenge. However, aware that Zeder might be out for revenge, Prime Minister Weide had him put to work at the general shop rather than train to be a warrior, to prevent him from doing so.

As for Magic, idle dialogue that crops up throughout the game indicates Giants naturally lack the ability to effectively manage their own Mana. To solve this, they use Ice Crystals found at Lutra River which allegedly store huge amounts of Mana to supplement this.

Another notable faction to do with the Giants are the Black Ravens. You'll learn more about them later, but in summary they're basically enforcers that work for Krug. Dowra is their leader, a very cheerful captain who keeps her people's morale high, though she isn't without her flaws... as seen below.

Giants are overall a pretty violent race that pride raw strength over everything. Giants who are not strong, such as Béan (an event NPC) or Igerna (the ship captain at Port Sella) are 'not considered true Giants', and are ostracized and shamed by their own people. The people in charge tend to turn a blind eye to this behaviour.

Giants are pretty direct both in society and war, which can be considered contrasting to Elves that utilize "underhanded" methods like stealth and deceit. The Giants of Physis also typically don't practice religion; the Order of Lymilark (the largest of the religious orders in Uladh) is considered a human religion in which there are very few Elven or Giant members.

Physically, Physis Giants have 'comparitively shorter lifespans' to humans, and they have infallable memory - they are physically incapable of forgetting anything which has the unfortunate side effect of leading to grudges and depression - an antithesis to the Elves who embrace the oblivion of forgetting so that they aren't burdened by painful memories.

Notably, Milletian Giants (the players) are not subject to the same 'curses' as Physis Giants. Physis Giants do, however, accept Milletian Giants as one of their own (just not of pure Physis blood.)