How should I go about beating these opponents (or can I not yet for some reason)? I just used a ton of accumulated experience points thinking that'd help (close to 2 million), but they're still kicking Julienne's tail. I noticed that Kain often only allows you to use one weapon, but there doesn't seem to be a way around that.

https://subeta.net/petinfo.php?petid=513121 Julienne's current stats

They’re just very tough. Kain is the easier one of the two, but Lukien is probably the hardest challenger on the site.

So let’s look at Kain first. He uses seven different icon types in his attacks (:dmg:earth::dmg:water::dmg🔥:dmg🧊:dmg:magma::dmg:light::dmg:wind:). I opted for Corrupted Shadow Sword (:block🔥:block:water::block🧊) and Hand of Goddessbane (:block:earth::block:light:) as my constants. Those two give pretty good coverage. If you boost Julienne's health to 9k you also get extra healing from the Sword when their health drops low.

Kain has freezing and stealing disabled, which frees up your mod crystal slots. You can either add more defense or more attack icons to your weapons. I’d probably opt for attack crystals to help the battle go more smoothly. They’ll also generate curses so even when he is blocking with his shields, you’ll still be able to get some damage through.

Just be very careful to watch your health when his curse is disabling one of your weapons so you can heal or block at the right times and not die.

Lukien is a huge pain and very difficult. However he does have one important weakness: he does not block dark icons (:dmg:dark:). I loaded up my constants with all Dark Eye of Royalty Crystals for extra damage. (I would probably use Maniacal Essence (:block:dark::block:wind:) + Natasha (:block🔥:block:light:) for him.)

Most of the early part of the battle is just about surviving and making sure you are healing or blocking at the right times. He does have a limit to his Potions of Phoenix and there are only about 10 or 11 of them. Once he uses all of them up, things get a little easier. I equipped a lot of healers (Reviver of the Lion, Phoenix Quill, Amulet of Drakkonis, Rage of the Paramnesia) to get through those battles. He really tests your skills and most people hate battling him :P

Oh and I just remembered, do not bring in Recycle Blaster and Soma Tablets for Lukien. He has too many weapons and they won’t have much effect. Fill those slots with something else!

Thank you so much!! I researched how to earn the Corrupted Shadow Sword as well as the Hand of Goddessbane and was able to get both! :)

With those weapons in combination with all my scrolls, so far, I managed to beat Lukien three times and Kain ten!

Congrats! That's awesome :D