How to increase the confidence index of a particular Hanagumi member?
I'm not sure if it's a deliberate feature of the game, but it seems that if one just goes along the game accumulating confidence points from the social interaction part, then in the beginning episodes it's very easy to have Sakura's confidence maxed, but very soon after other girls will take over, simply due to the fact that there are more social situations in their favor during the mid-episodes. And remember that episode 7 is the latest episode to determine who you'll end up with. Out of desperation, one may try to alter the confidence ranking by deliberately displeasing the girls who're ranked higher than Sakura, but this is not advised because it'll put the whole team in a disadvantageous postion during battle. One easy trick I found is to use the "Protect" mode of Oogami repeatedly on the member of your choice during battle. Whenever a Hanagumi member is attacked while under your protection (can only protect one member at a time), the confidence index for that member will increase by one. And since you can use up to 8 "Protect" moves during one battle, if you use them wisely (which includes sending the member of your choice into harm's way on purpose while she's under protection, not very ethical but it works ^_^;), you can increase whomever's confidence index by up to 8 points in one battle, which is usually more than what you can get during the social interactions in any one episode. A bonus is that neither Oogami nor the member you protect will suffer any damage when she's under normal attacks. I think I managed to increase Sakura's confidence index by something like 20 in the 3 battle segments in episode 3 alone using this trick ^_^
How to defeat those nasty end-bosses?
I don't think Sakura Taisen is particularly difficult when it comes to fighting end-bosses, but it could be frustrating when some Hanagumi members got fried by one of the bosses' "Sure-Kill" attacks and you have to start the battle all over again ^_^ So when fighting the later end bosses, make sure all members of your team have their health points and special-attack points maxed before approaching the end-bosses. Approach the end-boss together, and try to position your team members in the following pattern within the time of one or two moves: Oogami should be adjacent to Sakura (or whomever he can use combine-attack with) initially so they can use their combine-attack. Afterwards move him next to the end-boss for normal attacks. There can be variations to this pattern but the main point is that everyone should have the end-boss within their attack range (sure-kill and otherwise) and that Iris should have everybody within her sure-heal range (so that she can heal everyone after the end-boss' sure-kill attack). Throw everything you got at the end-boss once in place, i.e. sure-kill attacks should be used by everyone and combine-attacks should be used if possible. After that continue with normal attacks, and healing members with Iris' magic if necessary (use Iris' magic wisely,as you may not get a second chance ^_^). This worked for me with most stationary bosses (finished Tenkai with just one attempt ^_^), but could be tricky with the moving ones (need to corner them first, or alter the pattern above to surround the end-boss completely). Another thing to bear in mind is that everytime you attack an end-boss, you'll increase its special-attack points, so get ready to withdraw your team members if the end-boss' special-attack points are about to max out and your team is in no condition to take the wrath of its sure-kill attack.
There can be variations to this pattern but the main point is that everyone should have the end-boss within their attack range (sure-kill and otherwise) and that Iris should have everybody within her sure-heal range (so that she can heal everyone after the end-boss' sure-kill attack). Throw everything you got at the end-boss once in place, i.e. sure-kill attacks should be used by everyone and combine-attacks should be used if possible. After that continue with normal attacks, and healing members with Iris' magic if necessary (use Iris' magic wisely,as you may not get a second chance ^_^). This worked for me with most stationary bosses (finished Tenkai with just one attempt ^_^), but could be tricky with the moving ones (need to corner them first, or alter the pattern above to surround the end-boss completely). Another thing to bear in mind is that everytime you attack an end-boss, you'll increase its special-attack points, so get ready to withdraw your team members if the end-boss' special-attack points are about to max out and your team is in no condition to take the wrath of its sure-kill attack.
Some general random hints
More hints to come as they manifest themselves ... ^_^