Immortality, sometimes he shows as 0.0 instead of 0.1, possibly due to rounding if he has 1hp left
Probably.
5* rank 5 Herc has base 33227 health. If he was at 1 point health under immortality, then not only would that round to 0.0%, it would also round down to zero points out of 15000 as that would be below 0.5 points (which would round up to 1 point). So the attacker HP remaining bar would show 0 points (0.45 rounded down to zero) and 0.0% (0.003% rounded down to 0.0%).
If a champion dies, it shows KO. If it doesn't show KO, that's not a kill, even if the numbers show zeros.
Comments
5* rank 5 Herc has base 33227 health. If he was at 1 point health under immortality, then not only would that round to 0.0%, it would also round down to zero points out of 15000 as that would be below 0.5 points (which would round up to 1 point). So the attacker HP remaining bar would show 0 points (0.45 rounded down to zero) and 0.0% (0.003% rounded down to 0.0%).
If a champion dies, it shows KO. If it doesn't show KO, that's not a kill, even if the numbers show zeros.