I'm always curious about that too.
I wonder if there HAD been a female knight before but she died from jealousy or something so the blue dragon and his knight agreed it would be safer for women to not make a bond.
Or a female knight started a war between her and whomever the first knight took as a wife... does that make sense?(〜￣△￣)〜
I don't understand the second part
Ok, I was able to piece my brain together better.
So the second part.
I meant in a way that a women had become a female knight thinking it would give her the chance to marry the blue knight but he didn't except her since he already had someone he loved and the female knight became jealous and tried to kill the love interest of the blue knight.
That makes sense
I was re-reading the previous chapters and some things stuck out to me.
1.There has never been a female dragon rider
2. The Duke mentioned that dragons like women chapter 22
3. When the Duke asked white if Melissa could bond with a dragon, white didn't respond chapter 22
4. The Duke/white said that the words of the blue dragon is law even if it was from a previous blue dragon, it has to be followed regardless
5. Dragons cannot lie
So I believe that a previous blue dragon made a decree concerning female's bonding to dragons and White not responding to the Duke's question concerning Melissa bonding to a dragon, means that the blue dragon made a condition concerning a female's being allowed to bond with dragons.
So if I theorize, Melissa will bond with Blue (or certain condition) thus fufilling the set condition and then giving female's the right to bond with dragons