You can hide a part of your soul-energy from your opponents. For each skill level, 100+(your level * 2) becomes untouchable. This will not work when you are the attacker, or when the attacker's clan is at war with your clan.
If you're skill level is 5, you have 3000 SE on you and your level is 20, your opponent can steal 2300 of your SE, with 700 being hidden.
Learning level: 13
Max level: no limit