Reima’s Shards

I'm not sure if a Healer should even role-play interacting with Orion. As for the pros and cons:

Healer:
+The character can resurrect allies after a battle.
+The character has no reason to participate in battle; they can just hang out on the other side of the empire.
+Relatively large health pool, if you take "Strength of Spirit."
+Fast experience gain, as a result of high Wisdom.
+Essentially, only one characteristic is really important for performing their job well.
+In the long term, you can significantly buff party members with your training.
-Useless in battle; can't be anything more than support.
-There's a choice between buffs and heals.
-Buffs and heals are not just determined before battle, but at the beginning of the month.
-The origin bonus simply gives access to this skill branch.
-Doesn't look very good from a role-playing perspective.

Water Mage:
+Significantly more flexible compared to the Healer.
+Ability to remove negative effects or heal more often than the Healer.
+"Charges" for healing and removing effects scale with characteristics much better.
+Capable of not only healing when it comes to battle.
+Free origin bonus.
+Ability to expand the arsenal of abilities by studying other schools of magic.
+One of the starting items is, in fact, free skill points and outweighs most other options in terms of usefulness.
-Unable to resurrect allies.
-Buffs are absent as a fact, unless you study other schools of magic.
-Need to be present in battle.
-More fragile than the Healer and gains experience more slowly.
-Needs accuracy to be able to deal damage and is generally more dependent on characteristics.

I probably missed something, considering I'm sleepy and already nodding off. But I would choose the mage from this pair.

Added 1 minute ago

Can Arandor's Ikigai be discarded?

No. He didn't take the Discard conviction. And he didn't get onto the zero map, so that someone with that conviction could take his Ikigai.