Musashi D'eon synergy?

Waver would do since he can instantly charge Musashi's NP without having to rely on her Fifth Force A to pump her NP bar. D'eon is a tank yes, but her slot could have been used by a more useful servant that can provide her useful buffs or critical stars. And there's no other useful servant for Musashi to team up with and you know who he is.

P.S. Musashi doesn't need someone to tank damage for her since she alr got invincible skill. With Merlin, she is invulnerable on the most crucial moments except when the enemy's NP got invulnerable pierce and Merlin's NP is alr enough for her to take damage without suffering too much.

Musashi-D'eon synergy is rather bad since Musashi doesn't really need a tank support. Tank is only needed when you bring a fragile damager like a berserker. Musashi isn't fragile hence she doesn't need a tank.

As for Musashi's support, most general supports should work well with her. However, try to prioritize supports that can fix Musashi's NP gauge problem first before supports that boost her damage. Musashi's NP hits the hardest among all saber after all. Example of supports that can help Musashi's NP gauge problem would be: Nero Bride, Waver, Helena, and Shakespeare.

Adarkrevelation, they are not the best team up but still okay due to the fact of being a new player. But you should still use her to get free quartz for the time being. Just add other players for team support.

You do not have to say "I do not have a tank" or anything like that. You already have one of the best tanks in the game: Mash. I know not everybody likes her, but once you level her up (with skill obviously) she will become a life saver and most likely you will use her on hard battles as Nero Fest. Personally I recommend you give love to the best kohai

I think not quite need to have a taunt unit for Musashi except very taunt challenge quest you will face, or using combat unit just switch D'eon in (like enemy has invincible ignoring NP)

The good thing is that Musashi has somehow good survivability and debuff resistance even though she dont have healing. (if she need healing, then Hans/Merlin are good enough). I also feel good because her 3rd skill is independent to her best offensive buff (2nd skill), not like for Jalter and Jack, it is a thing whether to activate their evade/invincible skill to have best damage, or save it ti face enemy NP.

Also if you need a taunt unit, our Mashu is even better to have team-wide defence-up and attack-up for Musashi. And Leonidas if you can manage his np well, he also has lowest star weight.