Good End No. 6: Byakuren is a really nice person!
That's the message you receive when you beat Undefined Fantastic Object with Sanae-B. And she really, really is.

Byakuren's character is developed around her being "nice." She's essentially a friend to all living creatures, and her biggest goal is peace throughout the land. She prefers to settle conflicts with words rather than fists, and will avoid fighting unless absolutely necessary. She harbors a deep, motherly love for humans and youkai alike, and wishes for nothing more than their well-being and prosperity. She is deeply loyal to those in her care, and will always give you a spot in her heart. Second chances seem to be her MO, and she will go out of her way to help those in need--those called "lost cases" especially. Byakuren is full of empathy. Really. There's a huge chance she can relate to your tale of misfortune, and even if she cannot, she will sit and listen and give you her heart.

That doesn't make her a fragile flower, though. Byakuren will fiercely defend her ideals, as shown when she verbally shoots down the protagonist when they dismiss her offers of peace and equality. And like any other soul, she does get mad. It takes a whole lot to push her over the edge, but when you do expect her to snap rather violently...and then apologize profusely once she's calmed down. She can be ridiculously passive-aggressive at times, usually because of her intense beliefs in the first place, but as a whole this side of her isn't generally seen.

Though...being sealed in the demon world for 1,000 years ought to cause some damage on the mind, and for Byakuren it manifested in the form of ditziness. She sometimes doesn't quite get how the modern world works, and will often have nonsensical ideas to spout out. She often jumps to conclusions (whether they be good or bad), and goes with her assumption as the absolute truth until proven otherwise. She can be oblivious to things happening right under her nose, or obvious feelings of others.

But the base of Byakuren's existence was built around fear; fear of disappearing, specifically. She feared her own mortality, and she feared becoming useless. So despite her repenting, those fears still linger, albeit in trace amounts. She will not allow herself to die easily, but less from courage and more from that ever-present fear. The difference, though, is that it does not drive her. It is not the focus of her time. She has more important matters to attend to, and spending 1,000 years in Makai has hammered that lesson into her rather hard.

There's a common fan interpretation that Byakuren is an evil asshole bent on exterminating the entire human race for the safety of youkai. Although I think there's sometimes a mildly sinister undertone to her words, it's with good reason: the lady's hella old and spent most of her time in a world full of toxic miasma for air, maneating demons, completely alone, left to wonder what happened to the people she nearly spent her own life on saving, so she has a legitimate excuse for being mildly creepy at times, though nowhere near "evil." Otherwise, the "i spent 1000 years in makai and all i got was this cool scroll" factor just makes her a ditz, as I mentioned in the personality section.