Question about Excalibur

Hi, everyone. I'm in the beginning process of making a REM for the first time and decided on Excalibur. But I was just reading about the final product and have a question about the Addition Effect of adding damage based on your current HP. I'm guessing, as an "Additional Effect", it doesn't work with our Enspells, or at least the first tier.

If it doesn't work with Enspell I, does the additional effect work on subsequent hits if you're using Enspell II instead? Thanks for any help you can provide.

It takes priority over enspells, so if it activates enspells will not, if it doesn't then enspells will.

Great. Thanks for the info!