Boutique of the Relics

Boutique of the Relics (鍵の保管, Kagi no hokan: lit. Arsenal of Sealed Spells) is a Holder Type Magic Arthur invented himself after passing most of his key onto his son, Antoine Eugene Moshiyoto. Due to him losing nearly two dozens of Celestial Spirits, his arsenal of magic and spells has shrunk significantly, so he found a way a way to efficiently store most of their spells and recreate their effects later on. He later began collecting spells from his opponents' arsenals, making him adaptable to almost any type of Magic. The principle of this magic isn't quite simple, as it appears to be a mixture of Enchantment, Time and Space Magic. Using his Portal Genesis, Arthur creates a loop in the space-time continuum, which, simply said, contains the spell until he chooses to release it outside of the loop, with the same potential it had upon storing.

The medium for each of the spells is a key, and having acquired many Celestial Spirit Gate Keys in his past, in addition to these, commonly dubbed as Spell Relic Key (呪文遺物鍵, Jumon ibutsu kagi; lit. Charmed Misused Gateway), Arthur has gotten the title Man of Thousand Keys (千の鍵の男, Sen no kagi no otoko). The keys' size is roughly the same as the Celestial Spirit Gate Keys' but their designs can vary. Most of them resemble their sealed spell in terms of colour and overall design, the reason being the way each key is created. Although technically it could be any item, Arthur chose keys for this purpose due to him already being known as a wizard who uses keys, because it could simply be attributed to his primary choice of magic, Celestial Spirit Magic, without raising any questions.

In order to seal a spell, Arthur must first choose the medium for its containment. His choice is, of course, a simple plain palladium key which he usually forges himself. He then must proceed channeling his own ethernano into the said key, enchanting it and making it possible for the key to access previously created space-time loop. Upon opening the loop's gate, the key begins to levitate and absorb the ethernano heading towards it, sealing it within the mentioned time-space loop without any difficulties. In order to finish this process and shutting the loop, Arthur simply chants Seal! (書庫, Shoko; lit. Store the Energy) and the key returns to his hands, glowing. Approximately five seconds after the chant, the key's design changed, accordingly to the spell's nature.

Given that energy cannot be nor created nor destroyed, the spells stored within a loop remain of the same energy level, meaning its strength will remain equal to the moment the said spell was stored. After releasing the spell and unleashing its full potential, its ethernano is scattered across the place of its impact, and with the help of Time Magic it's brought back to the key itself without negating the spell's effect, as they are the aftereffect, rather than the effect itself of the same spell. Given this feat, each key can theoretically be used thousands of times, but thus far, Arthur has used a single key only twenty times, each time with the same strength as before.

The slayer aspect of Slayer Magics cannot be copied, but the effect itself can be replicated, as seen with Arthur successfully parrying his nephew's Tesentis with a replicated Water Dragon's Roar, as the previous has already proven its strength against the copied technique. It should also be noted that this technique cannot copy holder-type spells completely, just mimic their overall effect created by ethernano released from the magic item. Another limitation appears to be any type of Body Magic, such as Take Over, as that would require sealing of the caster as well. In addition, the Black Arts are also considered to be superior to this technique, as their energy can easily corrupt the key, consuming the space-time loop and breaking the spell. As Curses are in fact ethernano-based techniques, Arthur is even capable of storing Curses and using them later on, making him a rather versatile opponent.