Okay, you want to split hairs? Japanese words are not "spelled", they are written using a mix of Chinese and phonetic symbols. As noted above æ"å- is how one should write the Japanese word for "improvement". Unfortunately, many people outside East Asia has no idea how to read or pronounce that, so we "romanize" words based on a commonly accepted latin alphabet equivalent. The usual Latin alphabet equivalent is kaizen with a k. Lately, a lot of bars and brands in Japan are trying to use the 'c' instead of the 'k'-- the most common example is the NTT wireless provider Docomo (meaning "anywhere").
Here endeth the lesson.