(?)  \- Unsure/possibly not  
(\!)  \- Major idea  
(\!?) \- Morally grey or worded in a morally grey way  
(C: {c}) \- Clarification  
(r) \- This idea was originally intended but has been removed or changed

A story thing where the mc finds a way to use something or everything(\!) as a source for magic power by drawing the power into them first(\! Which could also naturally enlarge their mana reserve size by "stretching/training" it) as opposed to using it directly without storing it first. (r: mc could be a transfusion specialist in previous life if it's an isekai(?).) MC is the son of some sort of former hero(\!). This former hero could be disgraced or forgotten(?). This former hero taught them magic and battle along with all other roles needed for battle at a young age, however MC doesn’t know how to utilize power or has insufficient mana to cast spells(\!). Former hero parent could be of a different race secretly(EX: A demon king instead of a hero(?)) and/or the MC could be half elf or such.(?) MC uses mana stealing magic to achieve this goal and becomes OP by using object(s) mana. MC can safely take mana from humans as his ability to take mana from objects stemmed from his specialty of mana transfer – A common spell used by support specialties(\!). MC is party of a small party, who he gathers by randomly snatching them up if they seem interesting.(\!?)(C: MC does not kidnap people to be party members per se, however often “Grabs” or sudden and slightly forcefully(\!?) invites people to join their party) MC is not one fixed “party role” and can do major roles such a support(Healing/Mana transfer)(C: Support is their main role, however they can do the others at a lower level), tank, frontline fighter, archer, and mage.(C: Except for support and magic(Mage) they can do the other roles, however at a rank(AKA if their rank in magic is A, their rank in the others is B) lower)

START

Their steps echoed off the walls as they approached the large gilded black doors. 

(Continue: Door leads to boss room. He and childhood friend(F) try to fight first level boss, he runs out of mana quickly and his CH friend is throw aside, he struggles, almost dying, then figures out mana drawing ability, casts heal on self, shields CH Friend from mortal attack(CHF is already on ground dying), gets over to her, and injects mana into her system while healing her).

This could be followed(At some point) by him impulsive buying an elf slave(C: Close to the normal isekai trope, the elf would likely be a former warrior/war slave. He would just tell CHF that he’d go get a healer, and without context and before she can ask questions he goes, returns a couple of hours later with her in chains half in shock.)