Royal tomb - Oubo

Japanese: 王墓 - おうぼ

...refers to the practice of burying wives, concubines, and attendants in the tomb of a king or nobleman or other master as companions to the deceased, and the remains of such burial. Regardless of the size of the tomb, it is the tombs of the ruling class that are accompanied by burial with the deceased, and regardless of the level of power, they are called royal tombs, chief tombs, etc. It was a custom in an era when people believed in the existence of an afterlife, just like in each society (afterlife view), and according to ancient documents, there were cases where people were buried alive.

From [Imperial Tombs]

...In this regard, too, research into imperial tombs is lagging behind significantly.
[Royal Tombs and Imperial Tombs]
Let us list some examples of tombs that have been the subject of controversy in the past as tombs worthy of the title of imperial tomb, or tombs that show that large-scale funeral rites were performed. Well-known examples include the tombs of ancient emperors such as those of Ojin and Nintoku, the great tombs of the Shang Dynasty, imperial tombs from the Qin and Han dynasties onwards, imperial tombs from the Three Kingdoms period of Korea to the unification of Silla, the royal tombs of Ur and the tombs of the Third Dynasty of Ur in Western Asia, royal tombs of the Persian Empire, the Mausoleum at Halicarnassus, and the mastabas and pyramids of Egypt.

From the Yayoi Culture

...Thus marked the end of the bronze ritual vessels and the rituals of the Yayoi period.
[Communal Cemeteries and Royal Tombs]
Yayoi period graves were built in communal cemeteries. However, their appearance varied depending on the region and the era.

*Some of the terminology used to refer to "royal tombs" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…王侯貴族など主人の墓に，死者の供として妃妾や従者を同時に葬ること，およびその遺構をいう。墓の大小にかかわらず殉葬を伴うのは支配階級の墓であり，権力の大小は別にして，それらを王墓，首長墓などと呼んでいる。それぞれの社会と同じような来世の存在を信じていた時代の風習で(来世観)，古文献によると，生きながら埋められた場合もあった。…

【帝王陵】より

…この点も含めて，帝王陵の研究は大きく遅れている。
［王墓と帝王陵］
　帝王陵の名に値する墓として，あるいは大規模な葬送儀礼が行われたことを示す墓として，かつて問題にされた墓を列挙してみよう。応神，仁徳に代表される古代天皇陵，殷の大墓，秦漢帝国以降の帝陵，朝鮮三国時代から新羅統一時代にいたる陵墓，西アジアのウルの王墓とウル第3王朝の陵，ペルシア帝国の王陵，ハリカルナッソスのマウソレウム，エジプトのマスタバやピラミッドなどが著名である。…