This is a Killer-X.
Prelims
a) R12C1 = {49/58/67}, no 1,2,3
b) R12C2 = {15/24}
c) R3C12 = {69/78}
d) R7C34 = {39/48/57}, no 1,2,6
e) R8C23 = {29/38/47/56}, no 1
f) R89C4 = {39/48/57}, no 1,2,6
g) R8C67 = {15/24}
h) R9C23 = {19/28/37/46}, no 5
i) 10(3) cage at R6C4 = {127/136/145/235}, no 8,9
j) 41(8) cage at R5C5 = {12356789}, no 4
1a. 45 rule on N7 1 innie R7C3 = 5 -> R7C4 = 7, 5 placed for D/, clean-up: no 6 in R8C23, no 5 in R89C4
1b. 45 rule on N89 1 remaining innie R7C5 = 1 outie R6C9 + 2 -> R6C9 = {124}, R7C5 = {346}
1c. 45 rule on N8 3 remaining innies R7C5 + R89C6 = 9 = {126/135} (cannot be {234} which clashes with R89C4), no 4,8,9, 1 locked for C6 and N8, clean-up: no 2 in R6C9, no 2 in R8C7
1d. R7C5 = {36} -> no 3,6 in R9C6
1e. 45 rule on N89 3 outies R6C459 = 8 = {125/134}, no 6,7, 1 locked for R6
1f. 5 of {125} must be in R6C5 -> no 2 in R6C5
1g. 10(3) cage at R6C4 = {136/235} (cannot be {145} because R7C5 only contains 3,6), no 4
1h. 10(3) cage = {136/235}, CPE no 3 in R45C5
1i. 41(8) cage at R5C5 = {12356789}, 1 locked for R5
1j. 1 in N4 only in R4C123, locked for R4
2a. R12C1 = {49/58} (cannot be {67} which clashes R3C12), no 6,7
2b. Killer pair 4,5 in R12C1 and R12C2, 4 locked for N1
2c. Killer pair 8,9 in R12C1 and R3C12, locked for N1
2d. 45 rule on N1 3 innies R123C3 = 11 = {137/236}, 3 locked for C3, clean-up: no 8 in R8C2, no 7 in R9C2
3a. 45 rule on N4 2 innies R45C3 = 10 = [19]/{28/46}, no 7, no 9 in R4C3
3b. 45 rule on N4 3 outies R4C45 + R5C4 = 19 = {289/379/469/478/568}
3c. 2 of {289} must be in R45C4 (R45C4 cannot be {89} which clash with R89C4), no 2 in R4C5
3d. 29(5) cage must contain 9 in R4C45 + R5C34, CPE no 9 in R5C56
[Note. 29(5) contains 9 because R4C45 + R5C4 = {478/568} clash with R45C3 = {28/46}]
4. 45 rule on N3456789 2 outies R13C6 = 10 = {28/37/46}, no 5,9
5. 45 rule on C1 3 outies R347C2 = 20 = {389/479/569/578}, no 1,2
5a. 5 of {569} must be in R4C2 -> no 6 in R4C2
5b. 1 in C2 only in R12C2 = {15}
or R9C23 = [19]
-> R347C2 = {569} must be [956], no 6 in R3C2, clean-up: no 9 in R3C1
6. 45 rule on C12 3 outies R689C3 = 19 = {289/469/478}, no 1, clean-up: no 9 in R9C2
7. 45 rule on C9 2 innies R59C9 = 1 innie R4C8 + 10
7a. Min R4C8 = 2 -> min R59C9 = 12, no 1,2 in R59C9
7b. Max R59C9 = 17 -> max R4C8 = 7
8. R347C2 (step 5) = {389/479/569/578}, R12C1 (step 2a) = {49/58}, R12C2 = {15/24}, R3C12 = [69]/{78}
8a. Consider combinations for R12C1 = {49/58}
R12C1 = {49} => R12C2 = {15}, 5 locked for C2 => R347C2 = {389/479}
or R12C1 = {58} => R3C12 = [69] => R347C2 = {389/479/569}
-> R347C2 = {389/479/569}, 9 locked for C2, clean-up: no 2 in R8C3
8b. 17(3) cage at R5C2 = {278/359/368/458/467} (cannot be {269} which clashes with R45C3)
8c. 17(3) cage = {278/368/458/467} (cannot be {359} = {35}9 which clashes with R12C2 + R347C2), no 9
8d. 18(4) cage at R4C1 = {1278/1359/1467/2358/2367/2457/3456} (cannot be {1269/1368/1458/2349} which clash with R45C3)
8e. Hidden killer pair 1,9 in 18(4) cage and R45C3 for N4, 1,9 must both be in 18(4) cage or both in R45C3 = [19] -> 18(4) cage = {1359/2358/2367/2457/3456} (cannot be {1278/1467} which only contain 1 but not 9)
8f. 1 of {1359} must be in R4C1 -> no 9 in R4C1
9. R12C2 = {15/24}, R123C3 (step 2d) = {137/236}, R45C3 (step 3a) = [19]/{28/46}
9a. Consider placement for 1 in C3
R123C3 = {137}, 1 locked for N1 => R12C2 = {24}, 2 locked for C2
or R45C3 = [19]
-> R8C23 = [38]/{47}, no 2,9
9b. R9C23 = [19]/{28/46} (cannot be [37] which clashes with R8C23)
9c. R689C3 (step 6) = {289/469/478}
9d. 9 of {289/469} must be in R9C3 -> no 2,6 in R9C3, clean-up: no 4,8 in R9C2
9e. Consider combinations for 17(3) cage at R5C2 (step 8c) = {278/368/458/467}
17(3) cage = {278/458} and {467} with 6 in R56C2 => no 6 in R6C3 => R689C3 = {289/478}
or 17(3) cage = {368}, locked for N4 => R45C3 = [19] => R689C3 = {478}
or 17(3) cage = {47}6, 4,7 locked for C2 => R8C23 = [38] => R689C3 = {289/478}
-> R689C3 = {289/478}, no 6, 8 locked for C3
9f. R45C3 = [19]/{46}, no 2
10. 18(4) cage at R4C1 (step 8e) = {1359/2358/2367/2457/3456}}, R45C3 (step 9f) = [19]/{46}, R689C3 (step 9e) = {289/478}
10a. Consider combinations for R6C459 (step 1e) = {125/134}
R6C459 = {125}, 2 locked for R6 => R689C3 = {478}, 4 locked for C3 => R45C3 = [19]
or R6C459 = {134}, 3 locked for R6 => 41(8) cage at R5C5 = {12356789}, 3 locked for R5 => 3 in R4 only in 18(4) cage = {2358/2367/3456} (cannot be {1359} = [13]{59} which clashes with R12C1), no 1
-> no 1 in R4C1
[Almost cracked.]
10b. R4C3 = 1 (hidden single in N4), R5C3 = 9 => R4C45 + R5C4 (step 3b) = {478/568}, no 2,3, 8 locked for N5, R689C3 = {478}, no 2, 7 locked for C3
10c. 1 in N1 only in R12C2 = {15}, locked for C2, 5 locked for N1
10d. R12C1 = {49}, locked for C1, 9 locked for N1
10e. R3C12 = {78}, locked for R3, clean-up: no 2,3 in R1C6 (step 4)
10f. Killer pair 4,8 in R8C23 and R9C3, locked for N7
10g. R7C2 = 9 (hidden single in N7)
10h. R347C2 (step 5) = 20, R7C2 = 9 -> R34C2 = 11 = [74/83]
10i. Combined half-cage R34C2 + R8C2 = [743/834/837], 3 locked for C2
10j. 17(3) cage at R5C2 (step 8c) = {278/467}, 7 locked for N4
11. 16(4) cage at R2C3 = {2356} (only possible combination, cannot be {1249/1258/1348/1456} because R23C3 only contain 2,3,6), 5 locked for C4 and N2
11a. R4C45 + R5C4 (step 10b) = {478/568}
11b. 5,7 only in R4C5 -> R4C5 = {57}, R45C4 = {48/68}, 8 locked for C4
11c. R89C4 = {39}, locked for C4 and N8
11d. R7C5 = 6 -> R6C45 = 4 = [13], R6C9 = 4, 1 placed for D/
11e. 17(3) cage at R7C6 = {458} (only remaining combination), 5 locked for C5 and N8, clean-up: no 1 in R8C7
11f. R4C5 = 7 -> R45C4 = {48}, 4 locked for C4 and N5
11g. R5C5 = 2, placed for both diagonals
11h. Naked pair {12} in R89C6, 2 locked for C6, clean-up: no 8 in R1C6 (step 4)
11i. 5 in C6 only in R56C6, locked for 41(8) cage at R5C5
11j. 5 in N6 only in R4C789, locked for R4
11k. 4 in C3 only in R89C3, locked for N7, clean-up: no 7 in R8C3
11l. R6C3 = 7 (hidden single in C3) -> R56C2 = 10 = [46/82]
11m. Naked pair {48} in R5C24, 8 locked for R5
11n. R5C789 = {137} hidden triple in 41(8) cage, 3 locked for R5 and N6
12. 45 rule on R56789 3 remaining outies R4C124 = 15 = {348} (only remaining combination), no 2,6, 8 locked for R4
13. Naked triple {569} in R456C6, 6,9 locked for C6 -> R13C6 (step 4) = 10 = [73], R3C3 = 6, placed for D\
13a. 16(4) cage at R2C3 = {2356} -> R2C3 = 3, R1C34 = [26]
14. Consider position of 2 in C6
R8C6 = 2 => R8C7 = 4 => R8C23 = [38]
or R9C6 = 2 => R9C23 = [64] => R8C23 = [38]
-> R8C23 = [38], 3 placed for D/, R9C23 [64]
14a. R1C6 = 7, 3 in R1 only in R1C78 -> 25(4) cage at R1C6 = {3679} -> R2C8 = 6, placed for D/, R1C78 = {39}, 9 locked for R1 and N3
14b. R1C1 = 4, placed for D\, R1C2 = 5 (hidden single in R1) -> R2C2 = 1, placed for D\
14c. R3C7 = 4, R8C7 = 5 -> R8C6 = 1
and the rest is naked singles, without using the diagonals.