Before we get into details about fumikomi mechanism, I would like to talk about the word fumikomi.
Fumikomi is a noun form of "fumikomu", which means to "lunge" or "step in".
When the word "fumikomu" is used in daily conversation, it ususally has a sense of urgency or commitment.
For example, if you are new in a new environment such as work or college, you must fumikomu to the new world in order to get used to the new environment.
This "fumikomu" has a sense of commitment.
If you think about the real "kendo" situation, you have two real swords in front of you. When you step in, you may be chopped in half or you may chop your opponent in half.
Thus, when you step in, you must be determined. That is probably why we use "fumikomu" rather than just using "step in" or "jump in".
Anyway, this "fumikomi" thing is very hard for beginners to acquire. One of the reasons is that it is a very unusual movement for those who have never seen kendo before.
Thus, these people tend to think that fumikomi is a special technique. It is to be learnt but it is not too special to acquire at all.
There are two points to keep in mind.
These are the golden rules for beginners.
Just keep these in mind and practice fumikomi over and over again by watching the video.
Most beginners make fumikomi so difficult that they cannot even see what they are doing wrong.
If you want to see more videos on fumikomi, join Kendo For Life Study Group. There are videos dedicated to fumikomi.
Hope this can help.