Dragon's Dogma: Dark Arisen

This worked for me... much to my surprise.

Location: Entry to Fortress of Remembrance, from the Empty Corridor.
Vocation: Magick Archer
Weapon used: Dragon's Quickening (magick bow), 2 star enhanced
Skill: Magickal Gleam

Recommendation: do a "hard" save either at the repaired rift-stone in the Empty Corridor, or else up the stairs at Bitterblack harbor. It may take a few tries to make this work. Sometimes the mini-sun catches nearby, instead of going all the way to where Death hovers.

I strongly recommend that you do -not- have a lit lantern equipped by any member of the party. Those attract the reaper's attention, big time. It will quickly come to investigate a lit lantern (perhaps by teleportation), instead of hanging around where it needs to be for a one-shot attack to work.

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Alternatively...

Be a Ranger vocation wearing strength-enhancing gear, with the "Clout" and "Vehemence" augments equipped, and wielding a higher-end longbow (Veteran's Arc or better).

Conqueror's Periapts x 4 can also be helpful. (Such enhancements stack up to four. While it is possible to "use" more than that, they cease to add benefits.)

Use blast arrows, and Tenfold flurry. Aim between where the reaper's collarbone is, and its waist, when it does its scheduled appearance the first time one enters the Fortress of Remembrance from the Corridor of Emptiness.

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Using Magickal Gleam runs frustratingly unpredictable about where the mini-sun will appear. Sometimes it goes off about a body-length away from the Arisen, but other times it will actually hit the enemy.

When it hits undead, instead of merely going off near them, it can be devastating. Some are defeated outright, though others are merely knocked flat and receive a sizeable dent in their health. Since it can be so effective, it's often one of my equipped skills if I'm going anywhere the undead might be expected to appear.

Including Bitterblack Isle.

When Death appeared in the first room after the empty corridor, before running toward the door like a frightened child, I was curious to learn if Magickal Gleam would whittle down that menace as it did most other undead.

I fired one shot, which actually hit it. Boom! Death evaporated. I thought it was like those lightning-charged grabby ghosts, and expected it to re-coalesce shortly.

But it didn't.

My Arisen & Pawn each gained 4 complete levels (plus significant progress toward a fifth).

Someone else did a video of this variety of one-shot defeat of "Death" and posted it on Dragon's Dogma Wiki. It can be found on the page -- http://dragonsdogma.wikia.com/wiki/Death

Scroll far down the page, probably farther than you'd expect. Keep on going until you see two side-by-side videos of a blonde Arisen in a leather-look bikini. How it happened for me resembled the video titled, "Death slain with one shot (Magick Archer technique)" ...

(Well, aside from my Arisen looking completely different, and wearing a lot more armor...)

If the wiki write-up is correct, the Magickal Gleam technique stuns Death, and then it falls to its death in the bottomless fall just past the railing.

The next time I cleared enough of Biterblack Isle to reach the Empty Corridor, I did a checkpoint save in a riftstone, and then tried again. It took a few tries, but eventually it worked.

One must hit Death with Magickal Gleam while it is hovering on the far side of the railing. If it gets over solid ground (or water), instead of the abyss, it only remains stunned for a short time before renewing its search for prey.

After being stunned, if it "survives," it's likely to focus its search on the vicinity from which the shot was fired... (a good time to visit the pause screen, and "return to last checkpoint").

Hope the information helps someone else!