Had an idea for both Regieleki and Regidrago. To even access them the MC would need all the other regi's since they would be both in Regigigas main or biggest workshop complex in disrepair and need them all to even open the door like for Regigigas but meet stairs that go up and down for the two. For Regieleki would be up stairs toward Regigigas quarters or living area and eventualy find her still pluged into a electric massage chair that she is powering. Pretty much regigigas created her to be a mobile power source to power her appliances so she does not need to create power sources all the time. Regieleki is over charged and need to be drained of the excess energy with the help of the other regis in the battle. The way she talks could be different since parts of her system would have short circuited to still talk like a machine but have some personality since she was left on for so long and it developed. The reason why she was left there and on ties into regidrago not having enough material to finish so regigigas left and forgot to come back for some reason.
For regidrago would be a little complex, would be down the stairs to the workshop forge and be just the head that is extremely large. Once the MC sees the head the regis come out and the idea is that since regigigas never finished her she unconsciously remembers to modify her so she would need to go to sleep and she would sleep forge modify her to be same size as other units and look like a dragon girl. So the three regis would then be busy trying to wake regigigas again while MC battle regidrago and wins. Once won drago would fly to gigas and punch once to wake up her then make love to MC. She was made to be the best alarm clock for gigas.
The dream of Regigigas could be in the center of a volcano forge or sun forge and she would be creating her master piece and greatest creation. Using all her strength knowledge and will to make the perfect bed that will give the best sleep ever and never need another bed. Once done she gets in it and sleep for the rest of eternity.