I also have an older and younger siblings (I'm middle child) so I didn't feel any hate towards dojin even when he did that. Saying things in sweet ways was almost never a thing between us. And that's what I like since we'll know exactly what we did wrong and what we should improve immediately.
Amd I guess that's also what dojin did. It's true that what he did at first affected ajin negatively but later on I realized that he's just worried when he made that condition before giving the account back to her.
Ajin's life is slowly falling apart. The pressure and everything was weighting on her. So she needed that push from her brother even though it came out as harsh. Maybe her brother realized while using the account how the game and the people there affected Ajin in a good way and so he used that as her inspiration and motivation to do good in jer studies again.
Maybe that's just his way of worrying about his sister. Yes, I love doting brothers in historical manhwas because it's sweet to see. But siblings like dojin feels more like home. HAHAHAHAHA now there are two of us yapping in here lol
yes, i agreed with you. dojin's action feel more like home, i feels like he's my brother that's why i come to comment a long ass sweet message just to kinda protect him from the bashing. i'm acting like his big sister here because he really do remind me of my younger brother ╥﹏╥
(my brither is not as handsome and as brainy as him though, lolololo)
the other doting brother is sweet, yes, but sometimes it becomes cheesy and cringe. it's not that i hate it, but it's too much. dojin and ajin's siblinghood is how siblings toward each other, they are the NORMAL siblinghood. no matter how

The FL relationship with her brother is very realistic. my brother and i are like cat and dog, we cursed at each other, we physically fight, but still we're concerned with each other and help each one. just kinda explaining here that the brother's action is just normal toward sibling because some people may come to hate him huhu.
the brother is just concerned about his sister's future, the fact that he made a deal with her to keep the Ddea account because he know that she will do everything to keep the account because of the people she grown attached to made it already clear.
i don't know why i'm explaining it's just i find him sweet, not very sweet unlike the other brother in historical manhwa that is always over reacting. he kind of remind me of my brother 。°(°¯◠¯°)°。