"Nope... not gonna kill myself..." Ren managed to speak this through pained gasps, as this was clearly quite painful. Letting the energy build up at times and using other spells instead, like Mortal Demon's Flame. Since it had a longer casting time, more energy could build up during each cast. This demonic spell seemed to create some dark, powerful flame that was both eldritch and physical in quality. Ren was just using it to shoot powerful fireballs, this seeming to consume even more HP. Lucian would indeed need to use Healing Roots to heal Ren, but the moment he tried to connect his spirit to Ren as he would need to in order to use that power on Ren, Ren's eyes would widen. 

The power for healing roots would be consumed, consuming all of Lucian's usages of it, but before that corruption would spread to Lucian, Ren would throw him back with a Repulse Wave, Ren's HP starting to get pretty low. "Don't... do that..." he managed to gasp out, falling to his knees now. Luckily he still had his Runes. He used one, its healing not as effective as it should have been for some reason as the positive, healing qualities of the magic were somewhat pushed away. It still healed Ren somewhat, but not as much as it should have, but it allowed Ren to stand back up and stay alive. 

Ren had to use all of his runes in order to keep his HP from hitting 0 before the energy finally dispersed after one long minute. Ren fell back onto the ground, panting very heavily as he did so. "Damn... that hurt..." He looked quite exhausted. He barely had any energy to swipe the windows that appeared. "Ugh... sorry about your... power or whatever that was..." 

That had been an intense minute, Ren's HP having gotten dangerously low during that. It was clear that the ailment was powerful, but extremely dangerous.