Sneaking Into Teriu Part 2
Making their way back to Teriu, Kuromi made sure that Shiro took a rest so that her energy reserves could be replenished. The main problem of using Celestial Energy is that it is very limited and would only regenerate once you started to rest your body.
Sure it may be more powerful than mana but in terms of accessibility and efficiency, Kuromi still preferred mana over Celestial Energy.
However, there were some positives that came from this. Namely the fact that their enemies wouldn't be constantly reinforcing their bodies since the energy is limited. This gives them the opportunity to eliminate a large portion of enemies in an instant since without the reinforcement, they're essentially normal humans with slightly improved physical attributes.
In other words, they're babies with guns. As long as you deal with them quickly, they pose no threat.