Riku remained at the Tower for several days while Rachel prepared the spell. Sparring with his friends and learning more about being a Keyblade Master couldn't distract him completely from what he and Rachel were planning on doing and the consequences if anything went wrong.
Despite his feelings about what they were about to do, no one asked him if anything was wrong. Thankfully, he was good at keeping it to himself. Then Rachel came to the Tower to show Master Yen Sid the progress she'd made on a potion that had previously been a disaster. When she did, she gave Riku 'the nod'. He nodded in return.
The spell was ready