The Older birdman's plan

The reason he cared about Raweth's return was he doesn't want to see his little brother's suffering and amidst his suffering, he would occasionally say, 'Brother, where are you?'

Whenever he heard that pained voice, the masked birdman was unable to control his emotions; however, there was no cure for the poison in his body.

And he didn't care about the soundproof barrier that covered Krico's house as he could guess that Krico was once again starting his planning about something.

...

Inside Krico's house,

'Where are you Raweth? Please come back soon, I have some great plans for you,' Krico still believed that Raweth would come back to the tribe as he was the chosen one. 

And when he comes back, he could use his technique to transfer Raweth's talent, bloodline and cultivation into his own body.