There is nothing generic about what you want to do, as this request has no obvious basis in standard relational database manipulations. It requires a completely custom solution that will only apply to your data and thought process. It can be done, but you would have to elaborate on the rules and the full nature of your data to get a solution that works for more than this one example, since a manual solution would be my recommendation if this example was your actual complete data set.
There are several problems that have to be solved or rules that have to be understood.
1. There is no reason to assume that the features in FC1 are ordered in the sequence required to directly match FC2 as they are read, so the solution must overcome disorder in FC1.
2. Are the features in FC1 uniquely related to just one feature in FC2, or can the value in column one for any single feature in FC1 be found in the list of columns for more than one feature of FC2?
3. Are there two or more features in FC1 that have identical values in column 1? If so, how do you want them matched to FC2?
4, Is the list of columns in FC2 always alphabetically ordered according to alphabetic sorting rules?
5. Do you really need the letter stripped off after the first position in the list in column 2 of the output of FC2, or is "T1,T2,T3,T4" an acceptable output for FC2 column 2?
6. Is there always only one letter that is always "T" at the beginning of each value in column two of FC1 that has to be stripped off if it falls after the first position in the list of column 2 in FC2? Or are there other letters at the beginning of the values in FC1 column 2 that need to be retained if they differ from the item that precedes it in the FC2 column 2 list?
7. Is there a spatial join component to the problem where the features that are matched have to be in some proximity of each other in FC1 and FC2 before the column one values are related?
Other issues may become apparent as you explain your data and the rules governing a solution more fully.
In general, the solution will be through a python script that uses cursors and dictionaries or lists to read and manipulate the data from FC1 prior to being outputted to FC2. But the order of operations depends a lot on how you answer the questions above and any others that come up as you give more details on your problem.