If y'all wanna know, I got some ideas for fics:
[Alchemist in Fairy Tail] - Basically, SI (Not exactly full knowledge of cannon, just basics) with Absolute Transmutation with some restrictions, searching for a cure for his own chronic illness. The world seems to reject him- quite literally.
[Poisoned Elixir] - You already know what it is about.
[Devil of One Piece] - SI, MC simply appears in the world atop the Red Line... His abilities are basically weird, and he gets more of them. Basically Minecraft powers, makes a base in the center of the Red Line like an ant colony and fights against the Celestial Dragons. Get it? They're the "Gods" and he stays beneath them, like the "Devil".
[Arcanum Magus] - SI, this one has a few variants. I love the Dragon Prince magic system, and I really wanted to write it being more esoteric. I thought of putting an SI in at least three worlds: DC, One Piece, or HTTYD. The Arcanums would be Earth, Sky, Ocean, Stars, Moon, Sun, Rebirth (Life Aspect, Death Aspect, Change Aspect, Soul Aspect). I also thought how some Arcamums share what I like to call "aspect", which is a part or representation of a part of an Arcanum.
How the Sky and Ocean Arcanum share Ice magic with them- Looking at you, Aspiro Frigis and Terminus ad Glacium. The [One Piece] one is more "developed", with him not being aware of the plot of One Piece and being dragged into Ace's crew.
I also thought of this same character in Game of Thrones!
[YJ Pink Magic] - SI makes a bad wish, gets trapped inside a dimension of his own making learning a bunch of magic for who knows how long. He is an Anodite (From Ben 10) and can use magic. Eventually he appears in the YJ world. He is a bit insane, just a bit, because he spent a few hundred years alone.
[OP: Friendship] - SI gets a weird system that allows him to become friends with animals and beasts. His system allows him weird abilities related to the beings he is friends with, like making chimeras by breeding two beings of no relation to one another and somehow making a baby, getting blood mixed with other beings to get abilities, and essentially becoming the true King of Beasts. Somewhat in Rocks Era, a year or two before his death.
[Villain MHA Fic] - SI character with the Vocifery Ability. He's manipulative as fuck... Brainwashes Endeavor to be his "cute wife" (I mean, who wouldn't want him?) who obeys his every order, destroys civilization, and becomes ruler of Japan by sheer power.
[Rat King: DC] - Character is a fucked up little guy who survives being experimented on by the Joker. This fucks up his mind, gives him several agoraphobia and other problems... It also awakens his Meta Genes, which gives him super regeneration, which is what keeps him alive. He gets this [Template System] and gets the [Jurryrug] from Ben 10 and [Douglas Ramsey - Cipher] from Marvel. The limit of characters he can equip the template of is 3, and he needs to "absorb" the characters 100% before he can equip any others.
[DC Therapist] - DC SI who inhabits the body of his own self in DC that his job is Arkham Asylum therapist... Thankfully he's got this system to help him and he is also the candidate for a rather D-isfunctional family (wink wink), with the job to help the Batman Rogue Gallery, Batman himself, and other people from Gotham. Bring happiness and delight to others.
And some other ideas that I'll keep in mind :3