There are a great many things I could say about the relationship between (Japanese) jujitsu and (the more external styles of) aikido, so I'll start with this one. Aikido is the next register up from jujitsu in terms of them being linked and used at a similar range, and in that aikido can be used to augment jujitsu techniques. Conversely, jujitsu is not necessarily a register down from aikido, but is rather on a different register in that it is a fall-back for aikido. To elaborate, aikido principles can be relatively easily integrated into jujitsu techniques, even down to techniques as simple as using a basic Tomiki aikido pivot to take someone down from a clinch or pummel. Jujitsu on the other hand is useful to aikido practicioners in that for one, its gross muscle movements are simpler and easier to perform than aikido's finer and more complex techniques, making jujitsu an easily learned alternative for when fatigue or other variables set in. And in another point, when the opponent is able to jam or go to ground, aikido techniques perform on a limited basis at best, while jujitsu techniques excel.
   Some further points which bear more going into later:
-aikido takes a great deal of time to learn to apply, while jujitsu can be picked up very quickly.
-the majority of aikido's techniques are based on techniques while holding a sword - with aikido, sword movements are picked up very quickly, and can be used to augment one's understanding of the empty hand techniques
-interestingly in relation to that, jujitsu was originally for disarming an armored opponent with a weapon such as a sword; while modern Japanese jujitsu is more focused on countering styles akin to Western boxing, the links back to sword techniques are still there to be traced