having a killer instinct

barbarous callous cruel fierce grim harsh implacable inexorable inhumane relentless ruthless severe unforgiving unrelenting unsparing unyielding

unmerciful

compassionless cutthroat dog-eat-dog gratuitous hard hardhearted hatchet job iron-fisted mean machine mortal pitiless unappeasable uncalled-for unfeeling unflinching unpitying unsympathetic wanton

bright calm compassionate considerate easy feeling flexible gentle kind merciful mild nice peaceful polite remorseful sympathetic tender yielding

giving sparing