Number 9, is the Sephira Yesod [foundation] on the Qabalistic Tree of Life. The Nine of Cups, is Yesod in the Suit of water, and 9, being also the number of the Moon, strengthens Water. Thus the stability is restored to Water. After its wobbly exclusions to Hod (8-left hand path) to Netzach (7-right hand path) , the suit of Water has now returned to the Middle Pillar.
Astrologically Jupiter in Pisces is the Ruler of the 9 of Cups, thus adding a benediction that is more than sympathetic to Water. This is obvious, since Jupiter is the Planet of Chesed [Mercy} where water is in it highest manifestation. Plus, Pisces brings out the placidity of Water. The Nine of Cups is True Wisdom fulfilled in Perfect Happiness.
As you can see upon viewing of the Thoth card, there are nine cups arranged into a square, representing Chesed-Jupiter, overflowing and filling one another implying we have the most benevolent aspect of the force of Water;a pleasing state of stable and sparkling emotion.
The Rider-Waite 9 of Cups illustrates the more mundane meaning of The Lord of Material Happiness. The smiling figure is enjoying his complete success and fulfillment of wishes and proudly displays his wealth of nine golden cups in a moon-like cresent. The blue curtain represents the element of water.
When the 9 of Cups card is thrown during a divination, the querent is or will be experiencing:
The number 9 is also the number of completion. Happiness, is a sensationalizing of success and it's natural bonhomie is a hard one to find any negative connotations for. This is a pleasant card to have in your reading. However, in a Celtic Cross reading, it could be the first card description of the querent crossed by a negative card, such as the 5 or 7 of cups which would suggest why the querent isn't enjoying happiness. Otherwise, be happy!
Thank you for your interest and comments. May you live long and prosper.