The Boss is wearing red shirt which is why he named like that. He uses The bat'leth which is a double-sided scimitar weapon with a curved blade.
After defeating the boss, you receive a Blue Chest as a reward. Red Shirt may be defeated only once per timeline.
After defeating Red Shirt for the first time, you receive an achievement "Clear Area XIX" which multiplies non-tap monsters' DPS by 1.02.