The additional summoning skill on the Emperor's Sword could only be used for PVP and city raids. It was a fine weapon for PK battles, but when fighting monsters, the Ancient Kings and Imperial Guards it summoned would just stand there blankly without attacking.
The Mercenary Summons was the exact opposite of the Emperor's Summon. It only worked during PVE and was ridiculously useful against monsters, but it was practically useless in raids and PK battles.
Judging from the Mysterious Leader's tone, she was clearly deeply related to the demons. She stood on their side and said there were good and bad demons among them. What did that imply?
That she was either a demon herself, or that she was fond of demons. Those were the only two possibilities.