The information here comes from a post made by the official account on Hoyolab on 7 August 2024.

Allegedly, when the “Flaming Heart” Huaiyan saw this booklet and asked Yunli why she accepted the interview, Yunli simply replied:
“But they brought so many sweet and creamy pastries! Someone who carries sweet pastries and is willing to listen to what weapons have to say can't be a bad person, right?”

Since she started forging swords, she could hear the voices of all kinds of weapons.

Since his creation, he has been mature and silent, only speaking when necessary.

Join Yunli & Old Mettle in exploring the unknown “hot and cold” takes of weapons across the universe!

Yunli: When we first met, he was a massive broken iron sword, tall, blunt, and stubborn, rejecting heliobus, without a spine, and with an uneven crossguard.
We didn't get along back then… He said I had a bad temper, and I thought he looked ugly. But now? He says my sword skills are extraordinary, and I say he's unparalleled throughout history.

Old Mettle: (Yunli's Translation)
He urged us to move on to the next weapon now, he seems a bit shy. (=^-ω-^.

Yunli: Grandpa said that a sword has no fixed form. This bat of yours can be considered a kind of “sword,” reflecting your habits and personality. Let me guess, you're someone who… doesn't follow conventions, likes to improvise, and can face true enemies with calmness. Am I right?

Old Mettle: (Yunli's Translation)
Your bat also says it wants to rise to the zenith of Galactic Baseballerhood with you.

Trailblazer: Swing the bat, defeat enemies across the universe! Step out of your hometown, head towards conquering the stars! Rules are made to be broken!