1. Meta Knight developing a fat fetish because of Susie Haltmann and violently spazzing out and spilling his spaghetti in front of her because of it.
2. Susie cloning Meta Knight, having a secret underground facility on a obscure planet assimilated by HWC that's used as a farm for making more clones. Said clones are sold at a premium and used for anything you can imagine a sentient warm body could be used for. Meta Knight and Kirby find this, chaos ensues.
3. Meta Knight developing a fat fetish because of Sailor Waddle Dee and violently spazzing out and spilling his spaghetti in front of her because of it
4. Kirby developing a fat fetish because of Meta Knight and violently spazzing out and spilling his spaghetti in front of him.
5. Susie developing a fat fetish because of Meta Knight and violently spazzing out and spilling her spaghetti in front of him because of it.
6. Sailor Waddle Dee developing a fat fetish because of Meta Knight and violently spazzing out and spilling her spaghetti in front of him because of it.
7. Interspecies attraction between Susie Haltmann and a Kirbylike!Meta Knight.
8. Meta Knight whoring himself out.
9. Kirby whoring himself out.
10. Meta Knight and Kirby whoring themselves out.
11. Meta Knight taking Kirby on a romantic vacation to Mekkai.
12. King Dedede laying eggs, Kirby finds out, chaos ensues.
13. TKC Crew getting stuck in a dungeon that fattens them all up
14. TKC Crew getting stuck in a dungeon that wrings any and every bit of semen from the each of them until they are multi colored raisins.
15. TKC Crew's Sword Hero getting FUCKED by Meta Knight.
16. Kirby being a giga globe trotting planetary level slut.
17. Meta Knight having some sexual experience.
18. Meta Knight having absolutely zero sexual experience or knowledge and some character teaching him about sex. Hands on.
19. Kirby being a giga globe trotting planetary level slut and dating Ribbon (who doesn't know of Kirby's advanced 4D level chess sluttery).
20. Kirby and King Dedede raising a child.
21. Kirby and Bandana Waddle Dee raising a child.
22. Kirby and Meta Knight raising a child.
23. Meta Knight and Susie Haltmann raising a child.
24. Meta Knight and Sailor Waddle Dee raising a child.
25. Meta Knight and Galacta Knight raising a child.
26. Kirby and Galacta Knight raising a child.
27. Galacta Knight being released from the crystal and being """kept"""" by Meta Knight.
28. Galacta Knight being released from the crystal and engaging in the most reckless amount of hedonism imaginable.
29. Galacta Knight getting fat.
30. Meta Knight going to Kirby for unorthodox training.
31. Meta Knight getting DEEEP into looksmaxxing.
32. Meta Knight and King Dedede running for "King of Dream Land"

That's a fun question. However, before we can answer that it's important to note which kind of masochism you want Meta Knight to find joy in. I believe that masochism can be divided into categories.
- Physical Masochism (Meta Knight who becomes enlightened to the joys of pain and overstimulation.)
- Humiliation Masochism (Meta Knight who becomes enlightened to the joys of being humiliated and treated like an animal.)
- Submission Masochism (Meta Knight who becomes enlightened to the joys of servitude of someone higher than him.)
There are sub categories within these categories like 'Humiliation Masochism ➡ Being Treated Like a Pet Masochism'. I think for Meta Knight to be enlightened to any form of masochism you'd have to play off of his inherent traits and desires!
I think getting him to become a subservient masochist who loves following orders and being at the whims of another person can be done by playing into his desire to serve and protect as a knight, chivalry too if the person dominating him is a woman. If you can make this into something of a comfort of Meta Knight, a reason to let go of the high level of restrictions and standards he holds himself to, Meta Knight is more likely to submit.
As for physical masochism, I like the idea of Meta Knight being inherently impervious to pain or damage so pain as a sensation would be something alien to him, something exciting. I think if you combined pain with pleasure but slowly increased the amount of pain over pleasure Meta Knight would fold quickly and become addicted to such overstimulating sensations that he wouldn't be used to. It would be like alcohol, at first it's a little strong and even slightly nasty but the more you try it the more you want it.
As for humiliation masochism, that's super easy! You just need to break down his pride and his ego, and most importantly mix in some pleasure with that slow deterioration of his ego and pride. Most importantly, you must take advantage of Meta Knight's complexes like his desire to be seen as cool, manly, and strong! Similar to subservient masochism, if you can make it into something he can lose himself in he's likely to submit!

YEAH! So, this is very interesting...

Meta Knight has Sword and Blade join him on one of his excursions to adventure and train. For Meta Knight it's a very relaxing and meditative experience, for Sword and Blade it's more of a pain but they tough it out to be in Meta Knight's good graces. I can imagine Meta Knight's the type (on these special adventures) to go directly into more perilous or dangerous situations! So, upon seeing a cave with very obvious red flags that are practically screaming "DO NOT COME IN HERE IF YOU VALUE YOUR LIFE!!!!"

Meta Knight thinks "Hm, this seems fitting to explore."
Sword and Blade thinks "Nooo. NOOOO!!!"

But alas, Meta Knight has the two enter alongside him. Aided by the glow of Galaxia's light Meta Knight is in awe of the flora and wall carvings and paintings in this ancient cave. Beautiful bio-luminescent flowers sprout and blossom all over the walls, floors, and ceilings and there appears to be incomprehensible text dotting the cave walls too. He decides that he must delve in deeper! As they continue in further and further, Sword and Blade begin to feel something is up. It is as if there were more to this cave then what's being let on and there's this constant feeling of being watched that Meta Knight seems to be none the wiser. He's too enraptured with the surroundings, bless his heart!

Finally, the three make it to a clearing. There's an opening in the ceiling of the cave that lets in a beam of light that shines directly onto a huge flower. Now, Sword and Blade feel something is really up, especially with Meta Knight. He hasn't said much but when he does it's off. It's weird to say, but both the two knights-in-training take note of Meta Knight being too happy and way too relaxed for the situation. He fucking giggled. Meta Knight would never. Unbeknownst to the the three, the pollen that the glowing flowers release have a chemical to them that acts similar to a strong relaxant. It has no influence on Sword and Blade, but to seems to influence Meta Knight greatly. To Sword and Blade they smell something that's akin to burnt rubber, but to Meta Knight it's the most sweetest delightful scent imaginable! Meta Knight takes a step forward to the large flower, perhaps he could cut off a piece and take it back with him. Sword and Blade share a look, nod once, and begin to make a move towards Meta Knight. Upon putting a hand on Meta Knight's cauldron and saying that it's getting dark so they should head back to the base camp. Meta Knight flips decrying the mere idea of leaving such a nice place, he's lazily waving his Galaxia to ward the two off. Meta Knight then runs off and climbs the flower with the technique and agility of a fast drunken toddler. Sword and Blade go after him. Just as Meta Knight gets on the midpart of the flower the ground rumbles. Despite this Meta Knight lays back on the flower and drunkenly removes his mask allowing himself to deeply inhale more of the flower's scent and pollen, he feels really hot too so he removes his armor. Sword and Blade catch up and try to drag him off, but just as they grab him tendrils from the ground shoot up from the ground and surround the the three!

It was a trap, a deadly one at that as Sword takes notice of something...there's fur that looks very similar to some of the fauna around the cave littering the flower and the petals are particularly sticky and wet. Oh, stars. Oh fuck. This is a carnivorous one. Before Sword can warn Blade the flower closes around them. Trapping them in a warm, sticky pocket. This is fine, Blade thinks. He can just stab his way out with Sword. However, from the gaps between each petal tendrils enter. Priorities are changed and Sword and Blade focus on slicing as many of them as possible while protecting Meta Knight. However, being too focused on slicing up the seemingly endless barrage of tentacles, Meta Knight is grabbed. Sword and Blade flip and try to slice the tendril holding their master, but are hit from behind with something thick, heavy, and sharp -- another tendril that whipped itself directly at the two's heads. Rendering both unconscious.

Meta Knight lazily looks at the two, he wonders why they're sleeping. Perhaps....he should sleep too? That sounds like a good idea. It's so warm, and sweet in here. It's perfect for a nap. He wishes he could sleep but the tendril holding his body squeezes him, uncomfortably so, and another two restrain his hands. He can't nap like this! And another tendril enters his mouth, worms itself way down his throat. Meta Knight struggles weakly. It feels weird, but what can he do? He's zonked out of his mind on an au-natural flower opioid pheromone. So, he weakly tries to twist his body with little to no effect. It's painful...but then he tastes something sweet. It tastes like the most richest, sweetest, finest chocolate ganache possible. It's sickeningly sweet. So much is being pumped directly into his stomach that the vine's hold on his body starts feels painfully tight. No. It is getting painfully tight. Just when Meta Knight feels like he could pop like a tick, the hold on his body loosens, and the tendril pulls itself from his mouth. Meta Knight coughs, gags, and groans. Another tendril pulls his foot up while another begins to rub him down there. Meta Knight's face goes completely red. Wait...this isn't right....but it feels good...but it doesn't. His mind in a total state of confusion and drowsiness. The tendril wastes no time in entering him, thanks to the goo shot directly into his stomach, his body is loose and ready for some sex. Meta Knight would let out a lewd whine at the tendril ruthlessly pounds into him! The plant holds no restraint in violating Meta Knight. Another tendril joins in pounding his ass, and then another. It's too much, taking three tendrils all at once is way too much for the knight! Another tendril joins in to stroke, squeeze, and rub his neglected cock, pushing Meta Knight into the fast track for a white hot orgasm that makes him piss himself! The mouth that was whining, groaning, and moaning is quickly stuffed with a tendril who takes to throat fucking him hard. Even after Meta Knight orgasms, it doesn't relent.

Five hours pass.

Meta Knight is still being fucked. Luckily, Sword and Blade regain consciousness and are shocked with the sight before them. The tendrils busy raping Meta Knight's ass, mouth, cock, and urethra. Despite this, once Sword and Blade get their bearings they quickly jump into action. Expertly slicing, dicing, and stabbing the tentacles holding their master captive. Sword stabs the flower's center. It trembles before unfurling. The beast is dead! Meta Knight looks worse for wear. He's covered in a sticky burnt rubber smelling sap, his own semen, piss, and sweat. Meta Knight, thankfully still under the effects of the pollen, passes out once into a deep sleep once he's free. Sword and Blade carefully get him dressed and drag him out of the cave. Sword uses a communication device to have someone use one of the Halberd's aircrafts to get them back to the hangar quickly. Once they arrive, Meta Knight is quickly taken to the bathroom and washed up. Put into his comfortable silk night cap and put to bed.

As the effects of the pollen wears off when he wakes up, Meta Knight has a severe gap in his memory. He can't really remember what happened between entering the cave and waking up on the Halberd in his private quarters. His ass hurts, his dick feels sore, and he feels bloated. Sword and Blade decide to not tell Meta Knight and life carries on.

I can see it. Meta Knight is a man who keeps to himself, so I don't imagine he's easily accepting of being examined. Meta Knight would boast about how good in health he is, how important health is, and giving health tips to others but would admit he's never been to the doctors muchless have a physical. It's highly possible he could have gone decades upon decades without seeing a doctor, the mere idea of getting a physcial is completely alien to him. The closest he's been to a doctor is Sailor Waddle Dee patching him up after coming back from a deadly and deadly (but fun) excursion. The mere idea of a physical makes him hesitant, having someone examine and record such intimate and secretive details of himself (such as his weight) sounds like a recipe for trouble to him. I could maybe see him do it if someone he loved begged him to, otherwise Meta Knight won't go to the doctors willingly.

Mind if I  t y p e  a little?

Okay so, I'll order this list by ship contention. As follows; mtdd, mtsus, mtwd, mtkb

META KNIGHT AND KING DEDEDE
Romantic evening in! King Dedede has the Waddle Dees prepare his bedroom to be the ultimate stay-cation. He replaces the sheets and drapes with a nice valentines wine red, has a box of chocolates at the ready, chilled wine, and some movies he imported from Mecheye to watch.

META KNIGHT AND SUSIE
It's a fun day out! Meta Knight takes Susie to see the sights of Dream Land, trying out different cafes and shops! The have a nice brunch, walk around some of the towns that dot Dream Land, get ice cream, walk about some more. I can also see the two of them going to Merry Mago Land.

META KNIGHT AND SAILOR WADDLE DEE
Meta Knight sets up a romantic dinner under the starts and on the deck of the Halberd. He has Captain Vul fly the Halberd at a slow steady pace and at an altitiude that lets the both of them see the stars.

META KNIGHT AND KIRBY
Meta Knight decides to go all out, the both of them go on a trip to Mecheye! Meta Knight books a nice hotel with all sorts of neat things that wows Kirby (such as the bed spinning, or a hot tub in the bathroom), a reservation at a nice restaurant that he and Kirby eat at, and rents a car to cruise around with Kirby.

B-B-BONUS!!!

META KNIGHT AND GALACTA KNIGHT
They duke it out for five hours straight end then passionate sex for another three hours.

KING ANI!DEDEDE AND ESCARGOON
Escargoon takes King Dedede down to the beach to play with some sparklers! It's a pretty simple and impromptu date, mostly spurred on by King Dedede seeing some sparklers being advertised in Tuggle's store.