You can get an early lead on Ike provided you space your jolts well and get that single grab in. From the start, Ike most likely will have to approach.
However, an Ike plays this matchup correctly by powershielding those jolts and zoning you with jab and nair. Ike should not use fair that much onstage in this matchup, unless some necessary requirements are filled (you being offstage, or if you're on a platform or a position that would be hard to punish us).
Because Ike can zone pikachu fairly well with nair in the air and jab on the ground, pikachu must be very patient with timing QACs and relatively conservative when you decide to pressure us with aerials. 1 Jab could land anywhere from 16-->30+%, which puts pikachu at a disadvantage when he is trying to get the kill himself. Outright, jab and nair provides a solid defense against the majority of Pikachu's arsenal. Relying on well timed and quick approaches to breach this wall may prove to be quite challenging.
When you try to space your jolts, Ike would be ready to chase you to the far end of the stage. He will try to outprioritize you whenever you get close. On neutral stages with a platform or multiple platforms, this aids Ike immensely.
Offstage, pikachu has some tools to gimp Ike. Against a good Ike, tjolt should not gimp us, but it does guide us along a predictable path so you'll have a good guess of where and how we're going to aether.
If you're in a nice position, you may be able to tjolt Ike out of the apex of his aether. Otherwise, you should
1. Grab the ledge and hope he lands onstage or dies
2. Grab the ledge and quickly nair Ike while he is ascending with Aether (more effective at lower %s)
Even if Ike does not get gimped, he should still have fairly a hard time trying to recover if he is ever put into such a position (bad DI or good read from a CG). Unfortunately, you may be in this position only a few times in a set as long as Ike maintains proper DI, but that may be enough for you.
If the Ike avoids gimps, killing him amidst his jabs and neutral air could prove quite the challenge, especially if you wish to avoid getting killed at early percents. I think pikachu handles punishing Ike for his stronger smashes pretty well, so he may have to rely on tilts, aerials, and jabs, for much of the match. Because Pikachu can't easily pressure Ike with aerials, the Ike would know that you probably won't directly challenge him, otherwise... bad things may happen.
Ike loves platforms and smaller stages. He will probably ban FD or a similar stage. He will try to CP you Brinstar, Delfino, Battlefield, and other similar stages.
tl;dr version
From the start, avoid direct confrontation with Ike. Keep your lead and momentum over him. Go all out whenever he gets hit offstage, otherwise you may have to endure quite a frustrating match whenever any of you get close.
Hmmm.. I think the matchup may be slightly in Ike's favor.
