The Giants (巨人；kyojin) are an archetype introduced in BS03, and constantly has cards released in each era. Most cards in this archetype feature Fighting Spirit family Spirits which have blue skin, and hence, most cards in this archetype are Blue.
Rather than having a specific play style, the Giants are supposed to simply aesthetically refer to giant humanoids in the lore. It may be more suitable to call it a race. However, throughout the development of the card game, the Giants have two significant play styles.
The first play style involves the keyword Summon Bolt (For more information, you can also check The Pirates), which is possessed mainly by the Fighting Spirits. Some of these Spirits are "Giant"-named. However, the deck overall is already very niche, so it is near impossible to create a deck completely on the Giants and Summon Bolt.
The second play style came during the God-King era, this time involving the keyword Accel. Slightly better than Summon Bolt, a Blue Accel deck is plausible, but still very unstable comparing to other decks. These cards are often mixed with Yellow Accel cards, which allow a more versatile usage of the keyword.