This unusual condition afflicts mamonme from all phyla and families and yet is not inherent in all mamonme. It is usually displayed amongst urban dwellers, possibly due to the amount of humans and mamonme in residence in said civic regions. While in the past this behaviour was only apparent in friendly and neutral states, nowadays it is prevalent in small numbers in all boroughs.
It is said that those who are affected by this complex will usually meet a person they particularly like in their youth, however as they start to near their adolescent period, they will begin to subconsciously release a concoction of both pheromones influencing interest and disinterest in her "best friend". As a result the recipient of this strange amalgamation will see her only as a sister instead of as a potential lover. The mamonme will then claim that she is his sister and he her brother and will show him immense familial affection. This affection will more often than not, take the form of embraces, pats, hair ruffling and may even extend to actions which would be considered as leaning towards incestuous if the two had been siblings, such as "spoiling" her brother with lap cushions. What should be mentioned though is all of these actions will allow the aforementioned mamonme to gain spiritus from her "brother" through non carnal means.
Now while this may all seem a bit unfair for the recipient of these affections, the benefits include a loyal, protective sister figure who will oft attempt to set her "brother" up with a human partner who catches her and his eye. Now while she will not only bring about such a union, but also support it completely, as "sister" she will watch his partner's actions like a hawk and in most cases will even resort to "discreetly viewing" the woman's behaviour while away from her "brother." Woe betide the woman who attempts to dally with another male outside of her relationship. Such behaviour will lead to a quiet confrontation in a private area, and while it is unclear what these mamonme usually say, it is well known that those on the receiving end of a "chat" oft emerge tearful and extremely apologetic.
If the relationship progresses positively after this point, the man and woman will usually wed, after which the mamonme will find a partner nearby so that she may continue to keep an eye on her "brother's" wife while finding her own beau. If however the woman does not heed her warnings, and things do not go according to plan, the pheromones will cease and she will swoop in to claim her "brother" for herself.