What are these kill confirms. Can you list them? Are they generalized, or are they character, stage, position specific?
Some of these can kill lighter + floatier characters with poor DI.
Light weight + fast fall:
Uthrow->fair at the edge.
Uthrow->uair ~80-90% low rage
May also kill with nair at some % around 110.
Somewhat heavy characters:
dtilt->fair at the edge
dtilt->fair can kill on nearly all characters if they are dtilted at the ledge.
Most characters:
nair->fair at the edge
nair(backwards)->bair/uair
nair(sourspot)->bair/uair up to higher % than the above
dair(non-tech on grounded opponent)->aerial. Lower landing lag allows this to work now.
Reliable, but not a true combo:
jab->utilt
jab->dtilt->kill move
fthrow/bthrow->dash attack (non-tech)
force air dodge with nair/uair->utilt
force air dodge with nair/uair/fair/bair->dtilt->fair
Most of these combo on other characters and may still kill depending on the circumstances, just may be slightly out of reach at high % on the floaties sometimes or it may work just shy of kill %.
In general, Ike can kill with:
Bair, Fair, Uair, Dair, Ftilt, Utilt, eruption, aether spike, dthrow (rage), and dash attack most of the time.
Dash attack can't clank and the higher damage puts the opponent in stun more if it does clank, so Ike may be able to grab, dtilt, or maybe even utilt.
Even if something doesn't combo, uair lasts for 16 frames and kills. It's slightly better than 50/50 in Ike's favor if the opponent is ever popped up. Ike's air speed and QD allows him to follow opponents if he needs to. Even gimmick kills like fully charged QD may work on stages like final destination at 115-120%. Counter is there, may kill if tilts are countered at 105% at the edge, give or take 10 depending on the tilt.
It only takes a small read to kill with dash attack or usmash, especially dash attack. You can also just spam bair whenever you want near kill %. Ike doesn't need to change his game plan to kill anyone. It's easier to not go for confirms and just take the opportunity if it's available. All of his weaker moves have a chance to set up into other moves, and all the rest of the moves kill.