Mana Cage is one of the magical items described in Monster Girl Encyclopedia World Guide III: Sabbath Grimoire.
Guide Book Entry[edit]
A magical tool that can gather up the mamono mana that overflows from mamono and their partners when they join, and store it.
It is one of the most revolutionary magic tools devised and developed by the Mamono Lord's Army Sabbath. The existence of this magical tool has made it possible for the efficient and permanent recovery of "Mana Resources" used for all sorts of purposes such as magical research and experimentation, manufacturing magical tools and medicine, fuel for operating various magical devices that support Mamono Realm life, the production of large-scale spirit realms etc. Presently it is not only used by Sabbaths around the world, but also almost every Mamono Realm state, and even some mamono-friendly states, the total amount of mana that can be freely used due to the existence of this magic tool is hitherto incomparable, and it has become one of the major factors in the development of the Mamono Realm and mamono-friendly states.
Since the simplest of these "Mana Cages" are very inexpensive, they are sometimes offered free of charge from Sabbath and the state. By placing this in the bedroom during nightly coupling, the "Mana Resources" collected in the container can be sold by bringing it to a Sabbath or State that needs it, as well as the nearest Magical Tool Store that receives a mandate from them. The existence of this magic tool allows a mamono and her partner to obtain a minimum amount of money, even if they just spend their lives coupling.
In addition to the simple ones, various superior models exist such as those with enhanced mana gathering efficiency, and those that can compress collected mana which are more compact and suitable for carrying etc. Also, there are those that come with a technique to remove impurities, and can collect only the mana of a certain race from the air. There is demand for pure mana of a specific race for various magics and magical tools, and it also becomes things like medicines and perfumes for women who want to become a certain mamono or men who want to be liked by a specific mamono, it can be purchased as a high quality "Mana Resource" for a high price. Since these superior models use more advanced skills and techniques, they won't be handed out for free, you will need to save money to buy them, since purchasing them makes it easier to collect money, if you collect some amount of money with the simple ones, it would be nice to buy a high-end model. Since they become one of the interior pieces of the bedroom which is a love nest with their companion, for mamono, while the function is obviously important, the design is also considered an important factor, and there are also specialty magic shops that deal in a diverse variety of "Mana Cages".