#1 - Character Zeniths. Go to the character page. Most characters do not have it unlocked yet. Themed versions of characters can pool ZP together.

List of current zenith characters (not complete)
Gawain
Altair
Gandalf
Birdman
De La Fille
Lady Grey
Yuel
Lily
Light Sarunan
Cagliostro
Charlotta
Magisa
Wind Metera
Seruel
Io
Cerberus
Razia
S. Beato
Casual Zeta
Orchid

Notable SRs
Helnar
Gayne
W. Sutera
Soriz
Lyria
All story SRs

#2 - Seraphim Battles. Go to the Shop, then Weapon Series. You have to buy the initial SR for that element to get the fights (which are under special). You can only do 2 seraphim fights a day across all elements and difficulties. The SRs also require new treasures from the rotating elemental quests.

#3 - Rose Queen Weapons/Distinctions. Under Treasure Trade -> Treasure, you can trade for up to 10 distinctions (a month?) or trade for a rose, which is used in Rose Queen Weapons. Find those under the Quest Items tab.

#4 - Misc. You can use weapon skins for anything you have ever picked up (as long as it is the same type as the weapon you're wielding).