LN talks about it more but basically he's somehow a dhampir with a light attribute and chain magic/skill?
A dhampir, usually result of a human parent and vampire parent having a kid, has all the strengths and abilities of a vampire to a limited extent while stronger than a human. More human a dhampir is the weaker they are but also the stronger the resistance to a vampire's weaknesses like sunlight, garlic, light and holiness. Blade, for example, still needed blood, was strong enough to fight and kill vampires but wasn't bothered by sunlight and could enjoy eating human food. Or Rayne from Bloodrayne is strengthened by blood, doesn't poof in sunlight but still takes a fair amount of damage from it along with water.
As for the light attribute it not only allows him to use light magic and abilities but makes him immune to damage vampires would get from holy water, water, light, sunlight, holy attributed weapons (basically you stick him with a holy sword and it does no more or less damage than a steel sword of the same design,) so can go out in sunlight without being damaged or weakened. Light attribute is displayed as a giant black cross on his chest with the Chain showing up as chains wrapped around it like a tattoo. Don't know why they showed up like that but probably sign that he's either a hero or reincarnator or something big.
Basically MC is a daywalking dhampir immune to light and holy attributes that still needs blood occasionally but can draw nourishment from food as well while enjoying the taste.