I have this idea for a while hope you like it.
This is your Isekai story idea anyway this person end up in Monster Hunter by random portal or The famous Truck-kun.
They will get 2 or 1 ( if it too powerful except summoner abilities) abilities which includes:
Haki (all 3 but something has to awakened Conqueror like the big boss monster or the first 2 only)
Dragonslayer magic
The Six Powers
A Stand( No Star Platinum, Golden Experience, King Crimson or that undead stanf that creep me out too much seen this in a few stories you can use the other the stand or make your own up)
Devil Fruit
Chakra (With Tail-Beast or other naruto world abilities but real powerful ones must be awakened and try something with out kuruma you can use him but try like the one tail or something)
Keyblade(Normal)
Ki
Digimon (You gets a digimon pather and get more like in Digimon Xros Hunter with there a Digi Quarts and count as a summoer and have a fusion loader but it they phone and the digieggs for armor or orher stuff o they have to find)
Any Bleach Abilities
Summoner powers
Bender powers from avatar
For the super powerful abilities that you only choose one
All the Dragonslayer magic combine with other slayer magic
Conduit powers from Infamous Second Son
Ultra Instinct( it will be like Izuku from MHA/BNHA the OC will uses 1% because cant handed it yet they human not goku)
All of Ichigo's Powers( if you watch/read the anime/manga and play the game/app you know what i mean and he have to trained all of the and learn the the name of the sword even of the know it lile in the anime)
A System
The Ten-Tailed Beast with All of Tobi's Powers( Again cant used them right away and has to befriend the Ten-Tailed Trust like with Naruto and kuruma)
Keyblade with a system ( it will be let the kingdom hearts game you have to level up the get skills but has it will have 4 gachas one for skills(can be used weekly for free or with tickets or gems) summons(same as skills), weapons/items(daily free and money and for a better chance for a very rare one tickets or gems) and the final one is the chance of getting all the abilities, items and weapons (like goku the power pole and senzu beans through the senzu beans like a between 10 or 100 of them) of a character (monthly or special tickets each for a different type of rare like beginning kid goku or naruto for common and full powered ichigo or goku with all powers like Ssj4 ar UI be Ultra Legendary understand now)
Some things to make it more interesting
1 The OC will start in MHU3 combined with MHU4.
2 Will joined the Caravan crew and they will stay with them and the guild and travel all the way to the New World, Iceborne and Etc (and if he get the keyblade his tell them about the and they go to the other world with kingdom hearts world but add others)
3 Only if you choice keyblade the OC while help Sora, Riku and Kairi and be a big brother/sister to them and may changed the story abit.
Other stuff
Pairing
OC x Handler x Gulidmarm
For the kingdom hearts OC x Elsa x Anna x monster hunter girls
Let me know if you take the challenge i like to read it
(For me i would choose chakra with the sharingan and Vizard from bleach and for the 1 powerful ability the Keyblade with a system or All of Ichigo power or UI)