To be fair any kind of superpower is unrealistic. Since their power comes from the heart I assume it’s how our normal hearts function, they pump out blood throughout the body the same way their (iron heart per example) pumps out iron to use at will, regardless it is a bit funny seeing their abilities randomly manifest like the chains haha
Easy logic if you know science, this is why you listen in class. The heart probably "mutated" to have extra elements ( elements is what you see in a periodic table). The chains is probably a type of metal, and just the researcher's manifestation of that element, seeing how there's knives and sword... it's probably just variants or tiers. For regeneration, there's resurrection, and cactus healing. To tone it down for your comprehension, their superpower is science based as mentioned in the manhwa... and they have different variants that depends in the person's mutation. Invisibility is just refraction of light.
In my opinion, their powers are lazily written. Because, you involve the heart, one of the most important organs and somehow when activating the powers, it has no consequences? Where do the cactus spikes come from? How in the world is chains generating from his fingers? Also, the way they just fade out from his fingers is pretty funny. It's probably just fiction magic but it would have been fun to see scientific reasons.
-kangaroo