"A set of beliefs, values, and practises based on the teachings of a spiritual leader."
Check.
Check. 
Come all ye faithful... and devoted
Around this joyous Christmas season, we often focus on Christianity and forget that there are so many other religions out there with celebrations at this time of year. Today we look at the religion born out of the firm belief in Cloud and Aerith's love, Clerith.
Wait, it's not a religion you say? Oh, well, let's look at the dictionary.com definition of what a religion is:
Check. To be in the Clerith religion, you must believe in their love in the way it is listed above, as set by Analstar, their post-menopausal spiritual leader. Note how many times the word "beliefs" is used.
Let's look at other common practises of religious people.
Have a website for your church with your beliefs and events for the members.
Have a place of worship.
Sing hymns.
Check.
Apparently Clerith shipper is shorthand for Clerith worshipper.