Like Andrew, I think that this (fun and challenging) Killer shouldn't be called an Assassin since it's against our tradition and is in no relation to uA 99. So I was reluctant to post my wt, but Andrew convinced me to do so.
The most important move was step 5k which I don't look for too often but the candidate pattern at that stage led me to that move which is also the reason why I don't rate it 1.5.

Frank's 99.5 walkthrough:

1. C789
a) 22(3) = 9{58/67} -> 9 locked for N9
b) Innies N3 = 10(3) <> 8,9
c) 9 locked in R456C7 for N6
d) Innies N6 = 16(2) = [97] -> R6C7 = 9, R6C8 = 7
e) Outies C89 = 14(2) = {68} locked for C7+N6
f) 22(5) = {12379}
g) Innies+Outies N9: 6 = R8C7 - R7C7 -> R8C7 = (789)
h) 18(3) must have 8 or 9 and it's only possible @ R8C7 -> R8C7 <> 7
i) 18(3) <> 1 because (89) only possible @ R8C7
j) Innies+Outies N9: 6 = R8C7 - R7C7 -> R7C7 <> 1

2. R456
a) Innies R6789 = 13(2) = [85] -> R6C1 = 8, R6C9 = 5
b) 9(3) = {135} locked for C9+N6
c) Hidden Single: R9C8 = 1 @ N9 -> R89C9 = 10(2) = {28/46}
d) Innies N4 = 8(2) = {26} locked for R6+N4+20(5)
e) 14(3) = {158} locked for C1+N4
f) Hidden Single: R5C8 = 2 @ R5, R4C8 = 4
g) 22(3) = 9{58/67} -> 9 locked for R5+N5

3. C789 !
a) ! Innies+Outies C9: -7 = R1C8 - R37C9 -> R7C9 <> 7 (IOU)
b) 22(3) = {589} locked for N9, 5 locked for C8
c) 11(3) = {146} -> {46} locked for C9+N9
d) Naked triple (237) locked in R789C7 for C7
e) 19(3) = 9{28/37} -> 9 locked for N3
f) 13(3) = 1{48/57} because R12C7 = (145) -> 1 locked for N3 and R2C6 = (78)

4. C123+C5
a) Innies C12 = 19(3) = [946] -> R4C2 = 9, R5C2 = 4, R6C2 = 6
b) R6C3 = 2
c) Naked pair (37) locked in R45C3 for C3
d) 20(5) = 26{138/147/345} <> 9
e) Innies C5 = 22(3) = 9{58/67} -> 9 locked for C5
f) 13(3) @ C5 <> 5 because 5{17/26} blocked by Killer pairs (56,57) of Innies C5

5. R789 !
a) Innies+Outies N7: R7C3 = R8C4 = (1458)
b) 22(5) = {12379} -> 1 locked for C6, 2 locked for R7
c) 13(3) @ C5: R8C5 <> 7 because R67C5 <> 2
d) Innies R89 = 17(3) <> {467} because R8C9 = (46)
e) Killer pair (89) locked in Innies R89 + R8C6 for R8
f) Innies R89 = 17(3): R8C2 <> 1 because R8C58 <> 7
g) Innies N7 = 15(3) = {159/168/456}
h) 13(3) @ N7 = {238/247/346} <> 5,9 because {256} blocked by Killer pair (56) of Innies N7
i) Innies+Outies N7: R7C3 = R8C4 = (145)
j) 17(3): R7C2 <> 7 because 1 only possible there, R7C1 <> 2,8 and R8C2 <> 4,6
k) ! Outies R9 = 28(6): R8C1 <> 4,6 because:
- R8C1349 would be {1456} which forces R8C67 = {39} -> no combo for 18(3)

6. N78
a) 13(3) @ N7 = 2{38/47} because (46) only possible @ R9C1 -> 2 locked for N9
b) 17(3): R7C1 <> 7 because (69) only possible there
c) 7 locked in R7C45 for N8
d) Killer pair (89) locked in R8C6+16(3) for N8
e) 13(3) @ C5 = 4{27/36} -> 4 locked for C5
f) 1 locked in 15(3) @ R8 = 1{59/68} -> R9C3 = (89)
g) Innies N7 = 15(3) = 1{59/68} -> 1 locked for C3+N7
h) 5 locked in 16(3) @ R9 for N8 = 5{29/38}
i) Hidden Single: R9C9 = 6 @ R9, R8C9 = 4
j) Innies+Outies N7: R8C4 = R7C3 = 1
k) 20(5) = {12467} -> R6C4 = 4, R7C4 = 7

7. R9+R123
a) Hidden Single: R9C1 = 4 @ R9 -> R8C1+R9C2 = {27} locked for N7
b) Innies R12 = 9(3) = 1{26/35} -> 1 locked for R2
c) Hidden Single: R1C7 = 1 @ N3
d) 12(3) = {237} locked for N1
e) Innies+Outies N1: 1 = R2C4 - R3C3 -> R3C3 <> 6,9; R2C4 = (569)
f) Hidden Single: R7C5 = 4 @ N8, R6C5 = 3 -> R8C5 = 6
g) 10(3) = {127} locked for C5
h) 13(3) @ N1: R34C4 <> 8,9 because R3C3 >= 4
i) R8C3 = 5 -> R9C3 = 9

8. C456
a) Innies C1234 = 19(3) = 8{29/56}
b) Hidden Single: R3C4 = 3 @ C4
c) 13(3) = [436/832]
d) 5 locked in 18(3) @ R1 = 5{49/67} for N2
e) 19(3) = {469} -> R2C4 = 9, {46} locked for N1
f) 16(3) = {358} -> R9C6 = 3, {58} locked for N8

9. Rest is singles

Rating: Hard 1.25. I used combo analysis of Outies to crack it.