What? So Demon Lord Leon is into lolis!? *shocked and grossed out* He is after mask girl!...

No lol
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Leon is from earth and (i'm really sure) he was isekaid to that world along with chloe. They are childhood friends. He keeps on looking for Chloe that's why he keeps on summoning children. The reason why Shizu got isekaid too. He didn't know he and Chloe is in the same world now.

Childhood friend? But he's older? Or is it because of time difference between earth and isekai?

Maybe because of that.

Ok. But, explain the weird vive he gave out when he was gazing at her portrait. He gave: :Ah, my childhood friend and first love. Did the manga adapt differently from the light novel?

thats because they were isekaid into different eras at the same moment.

The manga did adapt correctly, it's just that the backstory hasn't arrived yet. And the manga put more details into visuals, so not everything gets explained much.

Spoiler!!
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Leon and Chloe got isekai'd at the same time as children, but then Chloe was immediately summoned into the present world. So Leon is just trying to find his missing childhood friend.

Remember, there are 3 ways to isekai into that world:
1) transmigration through natural dimensional cracks, like Yuki and Hinata.
2) summonings, like Shizu and the kids.
3) reincarnation, like Rimuru and Mariabel.

So the timeline would be:
1. Leon and Chloe isekai through method (1).
2. Chloe disappeared, summoned into the current era.
3. Leon desperately tried to search for her, even doing the illegal summoning ritual.
4. Because of him, a certain country did a lot of summonings, which ended up summoning Chloe into the current era (Leon has no knowledge of these illegal actions)
5. And that is why Leon and Chloe are of different age now.

That's just a very simple summary of their relationship. It could be said that Leon indirectly caused Chloe to be summoned.

He's a brocon ╮(￣▽￣)╭

Ah ok! That makes sense. Thank you

Thank Luminous, Leon ain't no Diddy!

Accthuallyyy.... **Insert nerd meme**

The correct term would be siscon. Because he has a complex towards a sister figure. Therefore, siscon. If Leon has a brother, then Leon would be a brocon.

Hope that helps!

More on this note. Spoiler!!
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Leon did know about the illegal summonings, but not ALL of them. When doing a summoning, most of the children, if not all, were considered "failed summonings". It's because usually their bodies cannot handle the amount of magicules entering them, obviously because of age. Hence the children almost dying before meeting Rimuru.

Leon did made a transaction with certain people who would make the summonings, however, those people did it a lot more than they should. And they didn't show Leon all of the people being summoned. It's mostly because they thought Leon wants the "failed" ones only, when actually he wants a certain individual only.

Basically, because the

More on this note. Spoiler!!
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Leon did know about the illegal summonings, but not ALL of them. When Leon did the summonings, he indirectly caused the method to be spread, of course illegally. As such, more than one parties did their own summonings, in the hopes of forcefully chaining a powerful Otherworlder to them. Example: the Otherworlders from Falmuth who rampaged at Tempest.

So, because more than one party did summonings, Chloe ended up being summoned by people unrelated to the organization that Leon did business with. As such, he doesn't know when Chloe arrived in the future, otherwise Chloe wouldn't be in that school in the first place.

(Also obviously no one knows that Leon is looking for a Chloe. They thought Leon is collecting "failed summonings" aka Otherworlder children, for military purposes.)