Lan Yu X Lan Chen (not related by blood, teacher-disciple romance, historical BL, 1,000+ year age gap, mind the tags)
Gentle, easygoing, almost godlike gong X obsessive, unhinged scholar and fanboy shou (later, his master will bring him thoroughly to heel)
Blurb: One day, an old ancestor is gravely injured in battle and forced to take the form of a child. A scholar finds him and takes him home. As it happens, the scholar is the old ancestor’s outer disciple.
Scholar: “Why were you there?”
Old ancestor: “I don’t know.” The truth might scare you to death.
Scholar: “Is that so? But today my beloved master and his direct disciple both went missing there.”
The old ancestor puts on a secret identity: “All right, actually, I’m that direct disciple. I was badly injured and turned into a child.”
Scholar: “Then where’s Master?”
The old ancestor lies without changing expression: “He said he was going somewhere to cultivate in seclusion, where nobody would know.”
Scholar: “Hmph. Don’t let me catch you lying to me.”
Old ancestor: ... I’m right in front of you. Whether you can figure it out is up to you.
One night:
Old ancestor: “Where are you going?”
Scholar: “To visit my master.”
The old ancestor suddenly gets the creeps: Hmph, you little brat. Just wait until I get my hands on you.
Theme: To be added.
More, please?