You have to beat the E4 exactly 100 times with a team of 6 Klefki, they have to have the nicknames K, l, e, etc. to spell out Klefki in your party.
Once you are done, go to Sycamore's lab and talk to him. He will then give you the Crest of Dedication, and upgrade your Mega Ring to become the Mega Pokévice.
After that, go beat the E4 again with your Klefkis. After that, they will finally Joint Shinka to become the Jingling Keys of Dedication, Klefkiichein.
You have to repeat the whole process, bar your conversation with Sycamore, 5 more times to create 6 Kelfkiicheins.
Once you have them, beat the E4 100 times with your team of 6 Klefkiicheins. After that, they will Joint Shinka again, into Klefkiicheinbokkusu.
You then have to beat your Rival in Kiloude with only Klefkiicheinbokkusu in your party, after you beat him/her, it will Modo Cheenji into Klefkiicheinbokkusu: Kiibureido Moodo.
With your Klefkiicheinbokkusu: Kiibureido Moodo you can finally go and open the Battle Maison door, behind which you will find Tentaquil
