From DoA ABJD Wiki
ReiTenshi are a special type of Volks Tenshi that are not available to be sold anywhere. Rather, Volks gives them away at events as a special prize for event-goers, usually via lottery or bingo, so that the recipients are chosen entirely at random.
They are a small Tenshi, coming in at around 10cm in size. They are only moderately poseable, having joints in their shoulders and hips only (no knee or elbow joints) and some of them have quite stylised poses. Some have their arms affixed in certain poses, while others have their legs entirely curled up. Only a few have ankle joints.
Like SeiTenshi, they have resin wings which are permanently attached and which come in a variety of colours including white and pink; however ReiTenshi wings are actually posable. Most ReiTenshi have different faces; there are a variety of headmolds available.
Because of ReiTenshi's lack of jointing, they would not meet the current criteria of on-topic on DoA. However, the ReiTenshi is grandfathered in and ca be posted on DoA.
The first ReiTenshi were released at Volks' SD Owners Thanksgiving Tour in Huis Ten Bosch, and were given away as a part of the lottery drawing held at the end of the event. Since then ReiTenshi have also been given away at each successive Dolpa, including NY Dolpa 2 (where a total of 10 were given away, the most ever so far) and it appears they will become a regular giveaway at Volks events along with SeiTenshi.
It is very rare to come across a ReiTenshi on the 2ndhand market as Volks gives them away as special gifts and frowns upon reselling them, and most owners believe it an honour to receive one and will not part with it.