The stepmom is still his stepmom.They are related through their dad since Takezou's mother was having an affair with big bro's dad even if they were both married.
At first I also thought that they may be only half brother, but 99.9% DNA test made me think that they probably real brother, the big bro may be just stepson of the first wife. I may be wrong. The truth is still revealed all. So we just wait & see.
The truth is still NOT revealed all. So we just wait & see.
...I think it doesn't make sense for them to be real full brothers at all.The test says "possibility of being related by blood:99.9%" it doesn't say if they're brothers,uncle,or whatever... even though we know they're obviously related at a sibling level.It says clearly in early chapters that Takezou's mother went to the big brother's father to get some money as they were having an affair for some times now.Later on, the two got married. The most probable is that the father was married to his wife that came from an equally respectable family but was seeing Takezou's mother, a married woman coming from a lower class, in secret.Eventually they officially got together either the father divorced his first wife or she died. We also know that the big bro was extremely close to his mother which is why he despised Takezou and his mother. I think it would make zero sense for him to be the child of Takezou's mother.
So yeah like you say we don't know what the author has in mind so you may be right, it would just be super weird in my opinion if they were full brothers instead of half.
I think big bro loved young bro but hated his stepmother or didn't accept her. The conflict in his mind caused him behaved strangely liked that.
Wife tried to hurt them back but... seemed like it effected in the opposite way.
If stepmother was actually his real mom, then the conflict was cleared. He could love his young bro with his whole heart that why he didn't blind himself on their last met.
I can't imagine what will happen to wife when she knows about her cute son.