A surprisingly decent combo (and definitely not just a result of me trying desperately to find a combo for Ranger and Monk):

Mr. Disintegration Pistol

Swiftstride Shifter Ranger 1/Monk (Kensei) 5/Ranger (Hunter) +2/Monk +12
Str 8/Dex 16/Con 13/Int 10/Wis 15/Cha 13

ASIs
5th: Crossbow Expert
11th: Sharpshooter
15th: +2 Dex
19th: +2 Dex

Ranger Options
Fighting Style: Archery
Hunter's Prey: Horde Breaker

Spells Known
At least one of Ensnaring Strike, Hail of Thorns, or Hunter's Mark, otherwise I dunno.

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So, your strategy here is to pick Hand Crossbows as your first ranged Kensei weapon. They basically let you fight like a normal Monk, except your range is up to 120ft. You'll use Kensei's shot for one level (4th level, to be exact), and never again, unless you're running out of ammo for some reason.

Now, the peak of this thing is at 14th level - that's when you pick up Sharpen The Blade. If you dump 3 ki into Sharpen The Blade, you end up with a +3 hand crossbow... which gives you an extra +5 to hit that you can trade away to Sharpshooter. Making 3-4 attacks per round that deal 1d8+16 damage each sounds pretty OK to me...

Honestly, though, you'd probably be better off trading those three levels in Ranger for a 1-level dip in Fighter. Horde Breaker is nice (as long as your enemies cluster a bit, you can match the number of attacks a normal Monk gets in melee), and the spells are pretty decent, but they delay your ASIs and cool Kensei stuff a little too much...