Sagittarius accents that part of your chart related to career, drive, ambitions, prestige, standing in the community and opportunity for success. The Jupiter of Sagittarius and your Neptune significator symbolize new starts, originality and a degree of selfishness. When together, you'll spread out and then perhaps join in one single line, representing an arrow that shoots directly for the mark.
Generally, the two signs are not considered compatible. But, if determined, this team could build together toward security.
For Pisces, Sagittarius could stimulate a fire, a drive which might otherwise be dormant. For Sagittarius, Pisces represents home and security. But there is conflict. The solution centers on deciding who is going to do the leading, who the following.
With Sagittarius, you will want to elevate your position. You'll want independence. You are more direct in your relationship with Sagittarius than is usually the case. There may be sharp rebukes connected with this relationship. There could be disagreements and battles. But, through it all, there is also likely to be progress.
Listen, Pisces: I would say this is a better relationship on the professional level than it is on a personal one. This means, of course, for starting a business, for promoting a product, for finding room at the top, this combination is favorable. But not so much so for peace, tranquility, emotional stability. There simply is apt to be too much conflict.
Of course, if you are both mature -and determined - then professional and personal success can be combined. But the odds are against it.
For beginning a project, for an original approach, for creative endeavors for these things -a Sagittarius is good for a Pisces. For emotional contentment, there might be much to be desired.