dragon
蛟 centers on a specific kind of dragon in East Asian mythology, often associated with water and floods. The given meaning 'dragon' is the core concept, with the character implying a serpentine water-dwelling creature.
蛟 combines 虫 (insect/reptile) with 交, which likely contributes the sound. The character refers to a mythical water dragon, and the 虫 radical is commonly used for serpentine or dragon-like creatures.
The insect radical 虫 often appears in characters for reptiles and dragons. Picture a dragon coiling like a serpent, with the right side 交 suggesting crossing or intertwining, like a dragon's twisting body.
For コウ, imagine a dragon coiling around a tall ancient tree: coiling -> コウ, and the dragon's body crosses and intertwines like the 交 component.