The Master Chief is an obvious choice. His stoic and powerful presence would be really interesting in the Skyrim setting. He could be like an otherworldly hero, and his Spartan abilities would make him a force to be reckoned with against Skyrim's foes.
The Dovahkiin, of course. Their ability to use the Thu'um (shouts) would be a unique power against Halo's enemies. And seeing how they interact with Halo's technology - filled world would be fascinating. For example, how would they react to a Warthog or a Scorpion tank?
Definitely Naruto himself. His energetic and determined personality would be a great contrast to the often more somber characters in Skyrim. Also, characters like Sasuke could be interesting. His brooding nature and powerful Sharingan abilities would make for some great interactions in Skyrim's dangerous world. And from Skyrim, the Dragonborn would be a must - include. The clash or cooperation between the Dragonborn's Thu'um and Naruto's jutsu would be really exciting to write about.
For the Naruto side, Rock Lee would be really cool. His taijutsu - only fighting style could be really different from what the Halo characters are used to. In Halo, the Arbiter could be an interesting character to include. His story of redemption and his unique combat skills could lead to some great storylines. And of course, Hinata could also be included. Her shy but strong - willed nature could be a nice addition. She might befriend some of the Halo characters and learn new ways to fight from them.
For the PJO side, Nico di Angelo could be a great character. His control over the dead could have some really strange and interesting interactions in Skyrim, where there are also undead creatures. On the Skyrim side, Ulfric Stormcloak or Elisif the Fair could be included. Elisif's leadership and Ulfric's military might could be factors when dealing with the demigods. If the demigods get involved in the civil war in Skyrim, their powers could completely change the balance of power. And Luke Castellan from PJO could also be an interesting character to bring in, as his complex personality could add a lot of drama to the crossover story.
The Prophet of Truth from Halo could also be an interesting addition. His devious plans and manipulative ways could create a lot of chaos in the Fallout universe as he tries to gain power over the different factions and their resources.
Definitely Dumbledore. His wisdom and powerful magic would be fascinating in the Skyrim setting. He could interact with the Greybeards and learn about their way of life. Harry himself would also be interesting as he could use his Gryffindor courage to face the challenges in Skyrim, like the dragons. And Hagrid would be great too. He could bond with the giants in Skyrim.
Definitely Master Chief from Halo. His skills and leadership would be a great addition to the Starship Troopers' universe. Also, Rico from Starship Troopers. He could learn a lot from Master Chief. Their interaction would be really interesting to see.
Definitely Percy Jackson himself. His ability to control water and his overall demigod powers would make for some really cool interactions in the Halo universe. He could be a bit of an outlier among the Spartans, but his courage and quick thinking would be assets. Also, Master Chief. His stoic and badass nature would contrast well with Percy's more impulsive and humorous side. When they team up, it would be an amazing duo to write about.
Seto Kaiba and Gary Oak would make for a fascinating pair in a crossover fanfic. Kaiba's arrogance and Gary's self - assuredness could lead to some intense rivalries. They might compete to see who can be the best in both the Yugioh and Pokemon worlds. Another interesting character would be Serena. Her kind - hearted nature could be a contrast to some of the more intense Yugioh characters. She could form bonds with the Duel Monsters in a different way than the other characters, perhaps using her compassion to calm down some of the more aggressive ones.
One idea could be that the Master Chief somehow gets transported to Skyrim. He could use his advanced combat skills and high - tech weaponry in the medieval - like setting of Skyrim. For example, facing off against dragons with his energy sword, creating a really cool contrast between the high - tech and the fantasy elements.
The Arbiter and Thor. Thor is a powerful Asgardian with his hammer and lightning powers, while the Arbiter is a skilled warrior from the Halo universe. They could fight side by side against a common enemy. Their different cultures and fighting styles would make for an exciting combination. Maybe Thor could teach the Arbiter about magic, and the Arbiter could show Thor some unique Covenant combat techniques.