red, anger, ire, surname
奭 centers on a vivid red color, often associated with intense emotion like anger or ire. The surname sense is a separate application of the character.
The historical origin of 奭 is uncertain. It appears to combine 大 (big) with a doubled 日/白 element, but the exact development is unclear.
Picture a large 大 person whose face turns bright red with anger, the doubled 日/白 shapes suggesting flushed cheeks.
For セキ, imagine a red-faced person shouting 'seki!' in anger: seki -> セキ, and the red color matches the meaning.