Special War Power (SWP) can be found under Daily -> Special War Power.
You can recruit Special War Partners here with the coupons you get in Hueco Mondo Attack (HMA). They can be upgraded to a better version which raises their attributes massively. Most partner coupons can be bought at level 61,71,81 etc. When recruited the partners will come 5 to 10 levels lower or higher than the Head Level depending on the partner. When upgrading the partners they will keep the same acquired mods, level of Evolution and level of Soul Cultivation.
Note: Some Partner require a certain Lead/VIP Lvl to recruit/upgrade them.
As you can see, there are currently 7 Partner available.