Unrelenting defenders of humanity, secluded, seeking hand to hand combat to end the enemy...i'd say executioners:
From the Forgeworld free pdf
"The Executioners (Progenitors: Imperial Fists)
Since the terrible lost age of the Scouring, the Executioners
have reaved a bloody chronicle across the history of the
Imperium, seeking out and slaying nightmarish threats and
foes uncounted. A macabre, proud and barbarous Chapter,
there is little now to connect them to their noble forebears
in the Imperial Fists Legion of old, save an unflinching will to
triumph and an unbreakable devotion to honour. It was debts
of honour that drove them to side with the Tyrant of Badab
during his rebellion, and honour once more which broke that
fealty and unleashed bloody ruin on the renegade in turn.
Bitter Mettle: All models with Chapter Tactics (Executioners)
ignore all negative modifiers to their Leadership values,
regardless of their cause.
Headhunters: All character models with this special rule inflict
Instant Death on a To Wound roll of 6 in a Challenge – roll
saves against these attacks separately. The character with
the highest WS (if two or more characters are tied, then the
controlling player must select one) in any assault with this
special rule must always issue a challenge in an assault if
possible."
From the Forgeworld free pdf
"The Executioners (Progenitors: Imperial Fists)
Since the terrible lost age of the Scouring, the Executioners
have reaved a bloody chronicle across the history of the
Imperium, seeking out and slaying nightmarish threats and
foes uncounted. A macabre, proud and barbarous Chapter,
there is little now to connect them to their noble forebears
in the Imperial Fists Legion of old, save an unflinching will to
triumph and an unbreakable devotion to honour. It was debts
of honour that drove them to side with the Tyrant of Badab
during his rebellion, and honour once more which broke that
fealty and unleashed bloody ruin on the renegade in turn.
Bitter Mettle: All models with Chapter Tactics (Executioners)
ignore all negative modifiers to their Leadership values,
regardless of their cause.
Headhunters: All character models with this special rule inflict
Instant Death on a To Wound roll of 6 in a Challenge – roll
saves against these attacks separately. The character with
the highest WS (if two or more characters are tied, then the
controlling player must select one) in any assault with this
special rule must always issue a challenge in an assault if
possible."
