"Taizokai is all about looking deep inside of yourself. It's like the micro-view of the universe. The kanji "taizokai" roughly translates to "the secret of the fetus". The concept is basically trying to bring yourself back to the most beginning form (like when you're still inside your mother's womb) and try to understand the universe at the most basic level. In other word, try to understand the meaning of life.
This stage of the practice contains a lot of visualization and is a huge jump from what I have been doing before. This is also consider as one of the most difficult part of my practice. At the end of my journey, around January, a ceremony will be done where I have to be blind-folded and throw a flower onto this mandala. Where the flower landed will represent how well my practices/meditation was during the next two months. Or many people believe it represents how do I shape my world (since each buddha represent a kind/set of wisdom, landing on which buddha represent what kind/set of wisdom one accumulate during the meditation process.) My mom was the only person ever, in our temple's history, who got the highest recognition for Taizokai. She landed right at the middle of the mandala. Talk about high pressure for me eh?
My master/sensei did gave everyone a personal tip for this stage of the practice, and mine was pretty interesting. Since he finds the major obstacle (or karma, if you fully understand what karma means) for me in my practice is that I seem to be not "growing up", he wanted me to visualize myself to be an old monk during the Taizokai practices. He wanted me to literally think that I am with white hair and wrinkles and doing practices. " - from Buddhist student blog