しつこく (translations)→ insistently keep naggingly narrowly pester stubbornly
仮借なく (translations)→ inexorable inexorably relentlessly
手きびしい (translations)→ attack blistering cruel scathing tough
情け容赦ない (translations)→ dog merciless
辛辣な (translations)→ acerbic acrimonious biting corrosive cutting mercilessly mordant peppery piquant tacky ungenerous vitriolic waspish
徹底した (translations)→ absoluteness deadly resounding tremendous
非情 (translations)→ bestial pain unfeeling
容赦なく (translations)→ brutal harshly let-down profoundly remorselessly ruthlessly surely unmercifully