Clad in holy garb, Rain Jewlitt - also recognized as the Methuselah - is a spaced-out, undying being who has existed for 624 years. Consequently, a generous reward is up for grabs for whoever can unravel the mystery behind his perpetual youth.
After the death of her grandfather, a sporty and vivacious Machika Balfaltin commences a quest to slay Methuselah, the lone bounty that eluded her ancestor Zol the Grim Reaper. Despite her original intentions, Machika repeatedly finds herself being saved by Rain as they evade other aspiring assassins who are vying for the prize.