It's been a while since I read this, & now I feel like I completely forgot & lost ...

It's been a while since I read this, & now I feel like I completely forgot & lost the plot, lol. So the younger brother is a bad guy? Why did they come to this place & how come Yurito suspects nothing? Why does he need to absorb energy again? Man, I don't even know how far I need to reread to be able to understand everything that's going on... ┗( T﹏T )┛