I found this information about ozoni styles from different regions in Japan:
Source: Honpa Honganji Hawaii Betsuin: Favorite Island Cookery Book 5, 1989.
Kanto District:
Soup: Sumashi Jiru (Clear soup)
Mochi: Kaku mochi, broiled
Other ingredients: Chicken, kamaboko, carrots, komatsuna, mitsuba, shiitake, koimo, daikon, chikuwa, horenso, gobo, hasu, kanpyo (tied in knots), kezuribushi, nori, mizuna.
Ingredients are boiled separately.
Tohoku District
Soup: Sumashi Jiru
Mochi: Kaku mochi, broiled; Fukushima: fresh mochi is torn up and put in soup.
Other ingredients: Chicken, gobo, koya dofu, carrots, komatsuna, salmon, zenmai, warabi, fuki, watercress, sasatakenoko, kamaboko, ikura, daikon, kaki (oyster), aburage, imogara, koimo.
Seafood is used alot because of its abundance in these areas.
Chubu District:
Soup: Sumashi Jiru, except in Fukui where aka (red) miso is used.
Mochi: Kaku mochi, broiled - Nagano, Niigata, Yamanashi;
Kaku mochi, boiled - Aichi, Gifu, Ishikawa, Shizuoka, Toyama.
Maru mochi boiled in soup - Fukui
Other ingredients: yaki dofu, daikon, konnyaku, ikura, koimo, buri, green onion, tofu, carrots, hakusai, kobumaki, iwashi no surimi, watercress, kezuribushi, komatsuna, chicken, nishime konbu, aburage.
Most of these areas cook the vegetables in the sumashi jiro and add mochi. When mochi is cooked, serve it with vegetables and cooked seafood as condiments.
Kinki District
Soup: red (aka) or white (shiro) miso is generally used except in Kita (north) Hyogo where sumashi jiru is prepared.
Mochi: Maru mochi, boiled
Other ingredients: Hamaguri, daikon, koimo, komatsuna, kashira imo, kezuribushi, carrots, kamaboko, yaki dofu, mitsuba, chicken, mizuna, gobo, konbu, yamaimo, tofu, shingiku.
Chugoku District
Soup: Sumashi jiru
Mochi: Maru mochi, boiled
Other ingredients: Shioburi, daikon, horenso, oyster, carrots, koimo, watercress, kokabu, kamaboko, iwa hagi nori, kezuribushi, konbu, anago, ko ebi, shiitake.
Iwa hagi nori, kezuribushi, Iriko, or buri is used for soup base.
Shimane's specialty is serving wasabi with the soup.
Tottori: Zenzai with mochi is eaten instead of ozoni.
Shikoku
Soup: red (aka) or white (shiro) miso and sumashi jiru.
Mochi: Maru mochi, an mochi, kaku mochi, boiled
Other ingredients: Daikon, koimo, carrots, tofu, buri, komatsuna, chicken, kamaboko, mizuna, shiitake, anago, usuyaki (sliced thinly) tamago.
Kagawa uses an mochi; buri is specialty in Southern Tokushima, Kochi uses various methods (West- Kanto style; East- fish ara as dashi); Ehime uses bright colored garnish.
Kyushu
Soup: Sumashi jiru and shiromiso shiru
Mochi: Maru mochi, boiled
Other ingredients: buri, daikon, yaki dofu, shiitake, makina, green onion, koimo, bean sprouts, chicken, surume, konbu, komatsuna, kuwai, kamaboko, gobo, mizuna, whole dried prawns, carrots.
Bean sprouts is specialty of Miyazaki and Kumamoto; Fukuoka and Nagasaki use a lot of different ingredients; Saga prefers it simple and refreshing.
Okinawa
Soup: Pork and katsuo bushi soup base
Mochi: Kaku mochi, broiled
Other ingredients: Belly pork, taka na (cabbage), daikon, usuyaki (sliced thinly) tamago.
Kanto style ozoni was adopted circa 1945.
Hokkaido
Soup: miso shiru
Mochi: Kaku mochi, broiled
Other ingredients: people migrated to Hokkaido from all different prefectures and brought with them thier regional recipes. Although preparation differs, salmon and ikura are used throughout Hokkaido. Specialties are shrimp, hokkigai, shiitake, daikon, salmon, and ikura.