The first Japanese Ultima maker is STARCRAFT. They were known as translator of Sierra adventure games. And they had released Ultima II and III at around 1984. Around 1996, they closed their company.
In 1986, Origin and PONICA signed a contract with Japanese porting of Ultima. The first Ultima that they released is EXODUS. They published Ultima I - VI for Japanese PCs, and most of Nintendo Ultimas. Now they were took over by their parent company, Ponycanyon, one of the biggest music publisher of Japan. FCI is also Ponycanyon's subsidiary.
Fujitsu is one of the biggest computer manufacturers in Japan. And they published overseas games for their PC, FM TOWNS. Ultima I - VI are published by Fujitsu.
Around 1994, a joint company of EA and Japanese electoric company Victor, Electronic Arts Victor(EAV) got publishing rights of Ultima in Japan. They published Underworld series, and Pagan for PCs, and Runes of Virtue II for Super Famicom(SNES in Japan). And at late 1997, Ultima Online was initially published by this company.
At Jan. 1, 1998, they changed their name into Electronic Arts KabushikiKaisha(EAKK, KabushikiKaisha=Co. Ltd.).
Then at Apr. 1, 1998, they became a joint company of EA and famous Japanese game publisher, Square. And their name changed into Electronic Arts Square. Ultima IX(initial release and earlier "EA Best Selections" release) and Ultima Collection(initial release) were published by this company.
And then, at Apr. 1, 2003, Square and EA terminated the joint venture, and the successor of the company, renamed into Electronic Arts KabushikiKaisha, is now owned by EA. Ultima IX(newer "EA Best Selections" release), Ultima Collection("EA Best Selections" releases and Ultima Complete were published by this company.
Locus had developed Ponycanyon version of Ultima games, and seemed to developed some EAV Ultima games. Also, they published Ultima cluebooks and Ultima novels!
Regrettably, in 2002, they decided to leave computer game business. At Feb 2009, they were closed by merging with Inforest Co., Ltd.. At December 21, 2016, Inforest were also closed by bankruptcy. Ultima Collection Japan Edition was re-released by EAKK after Locus ceased computer game business.
Must I explain this well-known company ?:-) They developed Fujitsu version of Ultima VI(Only English mode).
In fact, they are neither developer nor publisher of Japanese Ultima games. They are developped Ultima IV for NES; USA version. Around 2005, the company seemed to be closed.
A president of the company, Mari Miyazawa claimed in their another site that they had (at least partially) developed Ultima I,II,III,VI, and the Savage Empire for some Japanese PCs. They seem to be Ponycanyon version(Mari Miyazawa is credited in Ultima I, II and VI manuals). And a document in Ultima V box for FM TOWNS says they developed it.
In 2018, Miyazawa is known as a bento artist. Bentos(Japanese lunchbox) made by her look cute.
They developed following Ultimas.
Ultima IV for Famicom
Ultima V for NEC PC-9801 and SHARP X68000
Ultima VI for Super Famicom
Ultima Underworld for NEC PC-9801, FM TOWNS, and Playstation
Ultima Underworld II for NEC PC-9801 and FM TOWNS
Thinking Rabbit was well-known company as the original Sokoban. They developed Starcraft UltimaIII.
Their intellectual properties are owned by Falcon co, Ltd. and "Thinking Rabbit" is now their trademark.