FD/ other platform levels:
Get Ike to 40-60%, get him off the level (eg, backthrow from edge).
If he recovers from above ground level, height wise, hit him with a single-jump f-air.
If he's toward 30-45% at the beginning, you can try for a double-jump f-air. If he's kinda far off the level and hasn't used his double jump yet, then use homing attack.
This antirecovery move will leave Ike too far to recover, too low to recover, or just plain knock him off for the death.
;d
[edit]
If he's coming up from below the stage, you can try bombing him with springs lol.
Either way, if he loses his double jump, his recovery gets owned really badly- Aether has good vertical distance, but poor horizontal, and Quickdraw is good horizontal but useless if under the level.
For general fighting, try walking slightly out of range of his F-tilt: run in and grab, or roll behind and smash, or hyphen smash, etc after his attacks, and always be prepared to dodge a quickdraw, dashing attack or jab. I believe while trying Sonic out and fighting in a 'counter attack' manner, I had about 60% and 3 stocks by the time a lv 9 Ike was down to 1 life.