The Heavenly Lightning Bloodline is the innate bloodline possessed by all Heavenly Clans across the entire Starry Sky. Although there are many individuals across the Starry Sky who possess this powerful Bloodline, there are differences in strength and purity of each. The Demon Morph Clan, formerly known as the Yuwen Heavenly Clan, was publicly recognized as having the strongest and purest Heavenly Lightning Bloodline because of its Ancestor Yuwen Chenkong. However it has been shown that within the presumably trash Holy Light Galaxy, the Chu Heavenly Clan has birthed 3 generations of geniuses whose Heavenly Bloodline is so pure that it rivals Yuwen Chenkong's, and even surpasses his. It has also been proven that this is not the true limit of the Heavenly Lightning Bloodline, as it can still be evolved to a higher stage.
Heavenly Lightning Bloodline possessors have far superior Bloodline Talent (compared to Royal and Imperial Bloodline possessors) and they simply aren't present in Lower Realms (such as Ancestral Martial Lower Realm) and are scarce in Ordinary Realms (such as the Hundred Refining Ordinary Realm) due to the lack of effective/desirable resources for this bloodline.
The purity of a Heavenly Lightning Bloodline possessor's bloodline can be measured via the Nine Levels Heavenly Lightning Steps. The higher a bloodline possessor climbs on the steps, the higher the purity of their bloodline (the higher the talent of the bloodline possessor). Heavenly Lightning Clans (e.g. Chu Heavenly Clan, Li Heavenly Clan, Yu Heavenly Clan) will target individuals who have passed the 6th step, as a talent that requires key nurturing.
This bloodline's superiority is to the extent that Self Punishment Mysterious Arts have been devised to seal this bloodline's potential and have it gradually excavated as the bloodline possessor increases his/her cultivation realm.
The Bloodline Altar present in the Chu Heavenly Clan is simply one of the many methods used to help a Heavenly Lightning Bloodline possessor further comprehend their bloodline (and it's uses) and stimulate any latent bloodline talent, hence increasing their cultivation.