The "kuji in" are not something you can read about on the net or in a book and just start using them. As with everything in the martial arts you need an instructor. Simply sitting on the floor and saying the nine words while doing the nine symbols will do nothing for you. There is a progression to everything, you can't just start in the middle and expect any results.
Additionally i wouldn't take much information that site has to offer to heart. They are far from a legitimate form of ninjutsu. If you want to learn about the "kuji in" join one of the legit schools of ninjutsu, bujinkan, genbukan, jinenkan or toshindo.
Ninjutsu is also not thought of as an "internal" art. There are internal aspects to it, just like any other art, but it is an external art. For internal arts look to hsing i, bagua or taiji.
Enjoy life while you can, you never know when things will change.