I am asking on behalf of a friend who – while being a Muslim – for many years strayed from the path and didnt fulfil his religious obligations whether prayers or fasts. Only recently has he come back to practicing the faith, and has been working hard on making up for his past and genuinely reforming himself. However, one thing he is feeling hopeless about is making up missed fasts. He has calculated all his intentionally missed fasts for the month of Ramadan, and has come up with a personal number of having to either make up 8400 fasts as kaffarah (breaking a fast means fast 60 days) or feed 8400 poor Shia (60 people for each broken/missed fast). What should he do in this circumstance?

First he should make a will and then discuss with an aalim about the reaaons of leaving a fast. If the outcome is that they were left in a condition which make kaffara wajib he may start giving food to needy mominee slowly as per his capacity and start keeping the qaza fast.
Allah all kindness and all mercy.
Be sure He will not leave him just like that.