A boy's second chance

Upon dying at the First Siege, Wei Wuxian found himself back as a child. But at the moment that he met a younger Lan Zhan who gave him a toy drum one snowy night, and it had a profound effect on him. Why did he forget this moment in the past? A time when Lan Zhan wasn't the cold stuck-up he knew? He got curious and decided to return to the recesses a second time at 15 again.