I had kinda the same idea. I am not sure if he wants character dev of MC or the ones around him/her. I never read before The Novel's Extra so... should i guess he wants a novel where we see a character grow up and see the changes that occurs in personnality because of events ? Sure that sounds nice but i think 95% (random number) of the novels have a MC that is already grown up and already have a fixed personnality that won't change. Maybe Mushoku Tensei can be interesting to you. Also a novel on RR : The blue mage raised by dragons (not sure if it's the correct title), MC is kinda young, do mischief, think dragons can't lie so believe he is a dragon and follow the beliefs of them so maybe he will grow up and change, at least i hope so because i kinda hate the misunderstand (of him believing he is a dragon) and him doing mischief (like destroying the sacred tree of the elves). (Didn't get far, only checked the beginning). I think it's mostly a comedy novel. There is MAYBE also : Seven Unfortunate Lifetimes, All Thanks to a Single Moment of Impulse romance novel where MC and MF are fighting are the beginning and married at the end. 2 interlocked novels, pov of husband and wife: The Probability I Can Kill My Wife Without Being Found Out A Game To Make Him Fall At the beginning, husband is cold to his wife. Won't say more. The titles sound pretty dark but it's not, just a small accident happening and got a nice loveydovey (if we can call that loveydovey with how short it is, but now i think about it i would say YES) happy end. Edit : near forgot, there is also Savage Divinity (RR), romance is bad (they are fiance only / no sex), MC goes near death every month, MC had a happy life before transmigrating into a slave's body, MC suffer a ton if the near-situations were not enough, the world is a shit hole beside the people / village that welcome him (of course some exceptions like the friend that MC makes). Your choice to read it, too violent and dark for me.
Mother of Learning and Akuyaku Reijo Ni Koi Wo Shite (MC of those story is not real protagonist) Rakuin no Monshou Tales of Leo Attiel Legend of Galactic Heroes
Reign of the Hunters. Worth a read. MC was a bad person, repented and died and got reincarnated 10 years into the past. She then began a journey to correct her wrongdoings.