Futa momiji would be the logical way for them to make science babies. With Mahiro’s hips and breasts her being the one to carry the baby is a no brainer and the futa drug already exists canonically. If it can be used to make functional sperm then why not? How could Mahiro be more done for than by being plap plap plapped and impregnated?
schrodinger's cock n balls: We do not know who is wearing the pants in a relationship until they are in bed. Nor do we know their gender. Even if they are in bed.