Same as Before

"Who the hell are you calling mister tombstone?! Show some respect, ant!" Sure enough, it was none other than the altar with that 'being' inside. 

Rean wasn't lying when he said that he sent the altar into his spatial ring. After all, the situation was still dangerous, so the system was closed. He couldn't send the altar inside the Dimensional Realm. However, as soon as the altar entered the Dimensional Realm, all the influence of the 'being' inside it disappeared straight away! In other words, the Dimensional Realm considered the situation to not be dangerous anymore.

The twins truly intended to make the altar disappear when the spatial ring was broken. However, with the Dimensional Realm open, they thought it might have a better use if they sent the altar inside. One must remember that in the Dimensional Realm, Sister Orb was god. The being inside the altar simply had no power whatsoever in there.