「大鎧」即大型鎧甲，是日本鎧甲的代表，最早於十世紀出現，但一直到十二世紀左右才成為常用的鎧甲。為了減重，只有在重要的部位才用鐵製作，其餘則為皮製，或者以鐵片和皮革交錯運用；即使如此，整副鎧甲平均仍重達三十五公斤。大鎧不但巨大厚重，有許多部份也與人體形態貼合，因而阻礙揮舞武士刀時的流暢度，並不適合近身肉搏的步兵或槍兵使用。

由於日本幕府第八代將軍德川吉宗 (Tokugawa Yoshimune, 1684-1751) 委託製作許多鐮倉時期的大鎧，因此當時十分流行平安與鐮倉時期形式的復古大鎧；奇美典藏的這副鎧甲就是當時的代表作。整副大鎧都以罕見的棉包技術製作，以棉線為中央骨幹，外層包覆有花紋的絲線繩套。這是一種非常特殊的技巧，製作精細繁複，外表誇張華麗，只有富有的武士才能擁有，低階武士無法使用。頭盔上栩栩如生的飛龍極富設計巧思；木刻的飛龍保存良好，僅有少數維修痕跡，嵌有玻璃製的雙眼與金屬龍鬚，相當精美。

這件大鎧在江戶時期之後並沒有任何維修或變造，而且保存狀況完整且良好，可忠實呈現十八世紀日本鎧甲的製作工藝，因此擁有日本甲冑武具研究保存會 (N.K.B.K.H.K.) 頒布的證書，評定為「甲種特別貴重資料」 (意即『傑出的藝術品』)

O-yoroi refers to the large suits of armour worn by Japanese warriors as early as the 10th century, though they did not gain popular use for around another two centuries. In crafting O-yoroi, armourers would use metal plate on only the most critical portions of the armour to cut back on weight, leaving the rest to be covered with leather; alternatively, plate and leather could be interwoven to achieve the same effect. Even with a reduction in the overall use of plate, each suit of armour could weigh as much as 35 kilograms. Both heavy and thick, the O-yoroi was fitted to many parts of the human body and consequently hindered movement during battle. Hence, the O-yoroi was not used for infantry and spearmen.

Tokugawa Yoshimune (1684-1751), the eighth Shogun of the Tokugawa Shogunate, commissioned numerous reproduction of the Kamakura period, which resulted in a trend for retro-styled armour from the Heian and Kamakura periods. The O-yoroi currently in the Chimei collection is very representative of that period. It uses a rare silk-wrapping technique over the entire body of armour, which uses silk yarn to form the armour’s central skeleton, while the outer shell is covered with a decorative design, again using yarn. As one might assume, this is a very distinctive technique that incorporates many complex steps. Such embellished but beautifully-styled armour was only the property of the wealthiest samurai, as the lower classes had not the means to own or produce such exquisite pieces. The lifelike and opulent dragon design on the helmet is particularly inspired. Being carved of wood, the dragon is wonderfully preserved with only a small number of marks resulting from restoration. Inset with glass eyes and golden dragon-whiskers, the headpiece is truly a magnificent piece of art.

This particular O-yoroi did not undergo any restoration or alteration after the Edo period, and to this day the full set of armour has been kept intact and well-preserved, owing to the skill of Japanese armourers from the 18th century. As such, the Nihon Katchû Bugu Kenkyû Hozon Kai (NKBKHK, an armour society in Japan) has given this armour a certificate issued by the society which appraises it as an "outstanding piece of art".