Representing PT boats, which are too small a class for "shipgirlification", they appear as a trio of abyssal babies or even fetuses whose heads fuse into smaller versions of abyssal destroyer-types, like the I-class destroyer with large horns. One even has an apparent "umbilical cord" tube and a black diaper-like armor.
Like the ships they represent, they carry torpedoes as their primary armament. In-game they are made to be much harder for larger ships like battleships to hit unless they are armed with secondary guns, as they are meant to represent swarms of tiny coastal craft rather than individual ships.
They were introduced in the Fall 2015 event, which notably involves battles in the Solomon Islands Campaign where the US tried on several occasions to sink Japanese convoys with PT boat torpedo attacks, usually with unsuccessful results. They were quite successful though at "barge busting", attacking the barges and transports in the littorals as they tried to ferry supplies and reinforcements under the cover of night to avoid Allied air superiority. This helped to cause severe shortages of supplies and reinforcements for Japanese forces.
Their name can literally be read as "small oni group", so they might be considered similar to "oni-tier" ships.
